Submit post if user pressed Ctrl+Enter in reply content box
Using subscribed/unsubscribed for E-Mail notifications status

Earlier it was allowed/not allowed. It is just to help user understand
functionality easily
Renamed `Notifications` to `E-Mail notifications` for better understanding
Add explainatory title to E-Mail notification label in details meta box
Corrected WP coding standards
Order post by last updated with recently updated at top

Fixes #116
Echo dash sign if there is no respondent
Showing E-Mail acount of thread in "All threads" page
Reduced width of reply count column in all threads page
Reduced width of status column in all threads page
Showing excerpt of first reply in all thread page
Merge pull request #132 from VarunAgw/ux

Minor UX fixes:

* Add keyboard shortcut to submit a post
* Rename notification labels to improve clarity
* Show most recently updated posts at the top of the All Threads screen
* Add excerpts to All Threads screen