Primary key renaming

Improved consistency for existing core translation key names.

See flarum/core#265
- Completely overhauled core en.yml
- Replaced existing key names in all core JS files to match
- Extracted a hardcoded string in IndexPage.js
- Combined two app.trans calls in DiscussionControls.js
- Removed hardcoded spaces from LogInModal.js and SignUpModal.js
- Added two new keys from DiscussionControls.js (soft delete)
- Created two new “reused keys” to YML to accommodate same

js/forum/src/components/PostEdited.js

@@ -15,7 +15,7 @@ export default class PostEdited extends Component {
   view() {
     const post = this.props.post;
     const editUser = post.editUser();
-    const title = extractText(app.trans('core.post_edited', {user: editUser, ago: humanTime(post.editTime())}));
+    const title = extractText(app.trans('core.post_edited_tooltip', {user: editUser, ago: humanTime(post.editTime())}));
 
     return (
       <span className="PostEdited" title={title}>{icon('pencil')}</span>