Post editor quick win:

 * Remove paper airplane icon in ActionBar, replace with 'SAVE' or 'PUBLISH' text, depending on post status.
 * Save button is now visible on all EditPostActivity fragments.

Fixes #1339
Don't pop fragment if the activity is finishing.
Merge pull request #1388 from wordpress-mobile/issue/1339-post-save-button

Use text for Post Editor save button