Add Entry Headline and clear when creating new entry

[adamsilverstein]

Extends #473 with clearing of the headline editor when creating a new entry.

Fixes #375

Based on paulschreiber#17

• Add a headline field above the TinyMCE editor, (similar to LivePress).
• Headline field is optional.
• Store the headline in wp_comment meta.
• Send the headline over JSON as part of the API request for updates.
• Render the headline, if present, in EntryContainer.js
• php rendering for headline in liveblog-single-entry.php
• Clear headline after posting from main/top editor (track last update)
• Sync headline from data when using inline editor/editing exiting entries

[adamsilverstein]

Added the built files as well, @cain can you give this a test?

[cain]

@adamsilverstein Done some basic testing, seems to be working fine.

Whats everyones thoughts on using the headline as the key event widget content? Seems like it would be perfect and fix issue #464

[philipjohn]

Whats everyones thoughts on using the headline as the key event widget content? Seems like it would be perfect and fix issue #464

Yep, I think that'd be a good addition!

[GaryJones]

This is going to need to be rebased to be testable.