Unlocked notifications overhaul

[paulgibbs]

For 3.5, I want to re-work how the "unlocked achievement" notification popup is implemented. The existing approach was the very last thing I worked on for the initial 3.0 release, and while it worked, it wasn't particularly elegant in its approach or how it affected UX. See the tweaks to the persistence of the popup in the last few versions, for example :)

The main problems with the current implementation are:

• For unlocks triggered by front-end AJAX requests, you need to re-load the page to get the pop-up.
• In feedback-achievement-unlocked.php, the view and controller logic is all mixed together, making it both inelegant and hard to customise.

For 3.5, the new system (tentatively calling this "live notifications") has these features:

• Use WordPress' heartbeat API
• Use underscore.js' templating to render views from JSON data
• This will let us show the unlock notification as soon as an unlock happens
• This will also lay some groundwork to (in a future version) be able to trigger achievement events from JS.

[paulgibbs]

Trying to do a better job of tagging commits to a ticket, so here goes (in chronological order):

0e1c8c4957c595510978e7252d8e989d37b63472 2c0f89cf48dcf17022e8cf07870623a94b494547 060215d6ae62cafa3df10b9b96a5acbaafce6165 03301b401a6d49a88a4b45136f403d2b99268b14 4329ba31c21dcc19e503d3e2f4d40aa3433c36c3 17fd4ff5b02cd83a950d8e8ec235739d735a8215 1c7c08991ecb53515c1d46164614b1cacf58b851 0cb52881a0e2fbb76a96babaa3efb3240a9a4cd9

[paulgibbs]

15b3822531fe786ac0ecdf24199f663e559456b9 dd60d492bd21bc2ca8649ed8a32cc3b21483b54b 692b0b31561121429e7d811127d3929a186cea59 c6fe7b51e0206d5c625d19751374cfc9a06daa14

[paulgibbs]

Boom.