Don't autosave on focus-in to editor

Closes #4321
- Added a PostTitleInputComponent that sets its value to "(Untitled)" if it has no value on focusOut, and selects its text if its text is "(Untitled)" on a click.
- Removed autoSaveNew action firing onFocusIn of the markdown editor
- emberified the gh-trim-focus-input
- editor-base-controller is no longer responsible for setting a default title (horay!)