Mithril 2 update (#2255)

* Update frontend to Mithril 2

- Update Mithril version to v2.0.4
- Add Typescript typings for Mithril
- Rename "props" to "attrs"; "initProps" to "initAttrs"; "m.prop" to "m.stream"; "m.withAttr" to "utils/withAttr".
- Use Mithril 2's new lifecycle hooks
- SubtreeRetainer has been rewritten to be more useful for the new system
- Utils for forcing page re-initializations have been added (force attr in links, setRouteWithForcedRefresh util)
- Other mechanical changes, following the upgrade guide
- Remove some of the custom stuff in our Component base class
- Introduce "fragments" for non-components that control their own DOM
- Remove Mithril patches, introduce a few new ones (route attrs in <a>; 
- Redesign AlertManagerState `show` with 3 overloads: `show(children)`, `show(attrs, children)`, `show(componentClass, attrs, children)`
- The `affixedSidebar` util has been replaced with an `AffixedSidebar` component

Challenges:
- `children` and `tag` are now reserved, and can not be used as attr names
- Behavior of links to current page changed in Mithril. If moving to a page that is handled by the same component, the page component WILL NOT be re-initialized by default. Additional code to keep track of the current url is needed (See IndexPage, DiscussionPage, and UserPage for examples)
- Native Promise rejections are shown on console when not handled
- Instances of components can no longer be stored. The state pattern should be used instead.

Refs #1821.

Co-authored-by: Alexander Skvortsov <sasha.skvortsov109@gmail.com>
Co-authored-by: Matthew Kilgore <tankerkiller125@gmail.com>
Co-authored-by: Franz Liedke <franz@develophp.org>

js/src/forum/components/LogInModal.js

@@ -9,35 +9,35 @@ import ItemList from '../../common/utils/ItemList';
 /**
  * The `LogInModal` component displays a modal dialog with a login form.
  *
- * ### Props
+ * ### Attrs
  *
  * - `identification`
  * - `password`
  */
 export default class LogInModal extends Modal {
-  init() {
-    super.init();
+  oninit(vnode) {
+    super.oninit(vnode);
 
     /**
      * The value of the identification input.
      *
      * @type {Function}
      */
-    this.identification = m.prop(this.props.identification || '');
+    this.identification = m.stream(this.attrs.identification || '');
 
     /**
      * The value of the password input.
      *
      * @type {Function}
      */
-    this.password = m.prop(this.props.password || '');
+    this.password = m.stream(this.attrs.password || '');
 
     /**
      * The value of the remember me input.
      *
      * @type {Function}
      */
-    this.remember = m.prop(!!this.props.remember);
+    this.remember = m.stream(!!this.attrs.remember);
   }
 
   className() {
@@ -105,12 +105,14 @@ export default class LogInModal extends Modal {
     items.add(
       'submit',
       <div className="Form-group">
-        {Button.component({
-          className: 'Button Button--primary Button--block',
-          type: 'submit',
-          loading: this.loading,
-          children: app.translator.trans('core.forum.log_in.submit_button'),
-        })}
+        {Button.component(
+          {
+            className: 'Button Button--primary Button--block',
+            type: 'submit',
+            loading: this.loading,
+          },
+          app.translator.trans('core.forum.log_in.submit_button')
+        )}
       </div>,
       -10
     );
@@ -140,9 +142,9 @@ export default class LogInModal extends Modal {
    */
   forgotPassword() {
     const email = this.identification();
-    const props = email.indexOf('@') !== -1 ? { email } : undefined;
+    const attrs = email.indexOf('@') !== -1 ? { email } : undefined;
 
-    app.modal.show(ForgotPasswordModal, props);
+    app.modal.show(ForgotPasswordModal, attrs);
   }
 
   /**
@@ -152,11 +154,11 @@ export default class LogInModal extends Modal {
    * @public
    */
   signUp() {
-    const props = { password: this.password() };
+    const attrs = { password: this.password() };
     const identification = this.identification();
-    props[identification.indexOf('@') !== -1 ? 'email' : 'username'] = identification;
+    attrs[identification.indexOf('@') !== -1 ? 'email' : 'username'] = identification;
 
-    app.modal.show(SignUpModal, props);
+    app.modal.show(SignUpModal, attrs);
   }
 
   onready() {
@@ -179,7 +181,7 @@ export default class LogInModal extends Modal {
 
   onerror(error) {
     if (error.status === 401) {
-      error.alert.children = app.translator.trans('core.forum.log_in.invalid_login_message');
+      error.alert.content = app.translator.trans('core.forum.log_in.invalid_login_message');
     }
 
     super.onerror(error);