Bug 1077996 - Allow disabling Loop FxA support and related items (contacts, direct calling) via loop.fxa.enabled. r=mikedeboer

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extra : rebase_source : 99b0d348b6725c35c048a491e83c65e5b5e1b13d
Bug 1016434 - Backout of bug 759252 from mozilla-beta for blurry throbbers.
Merge m-c to fx-team
Merge fx-team to m-c. a=merge