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/DiscussionListItem.js

@@ -87,7 +87,7 @@ export default class DiscussionListItem extends Component {
         <div className={'DiscussionListItem-content Slidable-content' + (isUnread ? ' unread' : '') + (isRead ? ' read' : '')}>
           <a href={startUser ? app.route.user(startUser) : '#'}
             className="DiscussionListItem-author"
-            title={extractText(app.trans('core.discussion_started', {user: startUser, ago: humanTime(discussion.startTime())}))}
+            title={extractText(app.trans('core.discussion_list_started_text', {user: startUser, ago: humanTime(discussion.startTime())}))}
             config={function(element) {
               $(element).tooltip({placement: 'right'});
               m.route.apply(this, arguments);
@@ -108,7 +108,7 @@ export default class DiscussionListItem extends Component {
 
           <span className="DiscussionListItem-count"
             onclick={this.markAsRead.bind(this)}
-            title={showUnread ? app.trans('core.mark_as_read') : ''}>
+            title={showUnread ? app.trans('core.discussion_list_mark_as_read_tooltip') : ''}>
             {abbreviateNumber(discussion[showUnread ? 'unreadCount' : 'repliesCount']())}
           </span>