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/NotificationGrid.js

@@ -21,8 +21,8 @@ export default class NotificationGrid extends Component {
      * @type {Array}
      */
     this.methods = [
-      {name: 'alert', icon: 'bell', label: app.trans('core.alert')},
-      {name: 'email', icon: 'envelope-o', label: app.trans('core.email')}
+      {name: 'alert', icon: 'bell', label: app.trans('core.settings_notify_by_web_heading')},
+      {name: 'email', icon: 'envelope-o', label: app.trans('core.settings_notify_by_email_heading')}
     ];
 
     /**
@@ -182,7 +182,7 @@ export default class NotificationGrid extends Component {
     items.add('discussionRenamed', {
       name: 'discussionRenamed',
       icon: 'pencil',
-      label: app.trans('core.notify_discussion_renamed')
+      label: app.trans('core.settings_notify_discussion_renamed_label')
     });
 
     return items;