Store.Account#syncableAccounts
Show/hide sync button when account is added/removed
Merge branch 'bug-832258-hide-sync-button' of https://github.com/lightsofapollo/gaia into lightsofapollo-bug-832258-hide-sync-button

Conflicts:
	apps/calendar/js/views/settings.js
Merge pull request #13532 from gaye/lightsofapollo-bug-832258-hide-sync-button

Bug 832258 - Hide sync button r=gaye