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/EditPostComposer.js

@@ -23,8 +23,8 @@ export default class EditPostComposer extends ComposerBody {
   static initProps(props) {
     super.initProps(props);
 
-    props.submitLabel = props.submitLabel || app.trans('core.save_changes');
-    props.confirmExit = props.confirmExit || app.trans('core.confirm_discard_edit');
+    props.submitLabel = props.submitLabel || app.trans('core.composer_edit_submit_button');
+    props.confirmExit = props.confirmExit || app.trans('core.composer_edit_discard_confirmation');
     props.originalContent = props.originalContent || props.post.content();
     props.user = props.user || props.post.user();
 
@@ -39,7 +39,7 @@ export default class EditPostComposer extends ComposerBody {
       <h3>
         {icon('pencil')}{' '}
         <a href={app.route.discussion(post.discussion(), post.number())} config={m.route}>
-          {app.trans('core.editing_post', {number: post.number(), discussion: post.discussion().title()})}
+          {app.trans('core.composer_edit_post_link', {number: post.number(), discussion: post.discussion().title()})}
         </a>
       </h3>
     ));