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/TerminalPost.js

@@ -19,7 +19,8 @@ export default class TerminalPost extends Component {
 
     return (
       <span>
-        {app.trans('core.discussion_' + (lastPost ? 'replied' : 'started'), {
+        // Core Key Reorganization: Adjusted syntax for new key names 
+        {app.trans('core.discussion_list_' + (lastPost ? 'replied' : 'started') + '_text', {
           user,
           ago: humanTime(time)
         })}