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/PostMeta.js

@@ -33,7 +33,7 @@ export default class PostMeta extends Component {
         </a>
 
         <div className="Dropdown-menu dropdown-menu">
-          <span className="PostMeta-number">{app.trans('core.post_number', {number: post.number()})}</span>{' '}
+          <span className="PostMeta-number">{app.trans('core.post_number_tooltip', {number: post.number()})}</span>{' '}
           {fullTime(time)}
           {touch
             ? <a className="Button PostMeta-permalink" href={permalink}>{permalink}</a>