Check for extensions updates

Updated design

Check registry at most once a day

Remove updated and uninstalled extensions from update list

Use new icon sprite

Calculate when an actual update should be launched

Calculate updateCompatible for extensions

toggle icon even when registry are downloaded through extension manager

checkForUpdate is now called directly on the startup as it was before

combine the functions

download only if there're no updates available

delete icon that is no longer user

This sorts installed extensions by updateAvailable (#6634)

align = in exports

add an empty line

use localeCompare instead of ifs

use Array instead of array for preferences

do not convert new preferences

move event listener to the bottom of the file

move function to the bottom to make JSLint happy

count only compatible updates for notification icon

add comments

fix tests that were failing after changes to the model.notifyCount

fix issue when update button is disabled but newer compatible version (not latest) exists

add tests for ExtensionManager.getAvailableUpdates() method

add tests for ExtensionManager.cleanAvailableUpdates() method

move new tests
changes after review
Merge pull request #7330 from adobe/zaggino/check-for-update

Check for extensions updates