Comment tools overhaul

### Major Changes

* Preview and editor tools are now in separate modules.
* All features of the preview/editor are now supported on all markdown forms (including wikis).
* The user-defined macros can be separated into custom categories each with a separate dropdown.
* User-defined macros can now have custom keyboard shortcuts.
* Username autocompletion.
* Added a button to fade the Big Editor and allow the user to look at the post that they are responding to.

### Refinements and other changes.

* Open the Big Editor with `Control-e` and close it with `escape`.
* Keyboard focus is automatically moved where appropriate when opening/closing the Big Editor.
* The character counter has been repositioned for consistency.
* Pressing `escape` in a comment form will remove keyboard focus and return control to keyboardNav
* The autocomplete popup now appears to the right of the textarea so it can be usable