Bubble up error codes to devs (bug 846818)

This also cleans up the use of _error()
Merge pull request #293 from kumar303/errors

Bubble up error codes to devs (bug 846818)
Clarify who Bango is in developer message
Remove tracking event from poll() (bug 918877)
Merge pull request #295 from muffinresearch/remove-trackevent-from-poll-918877

Remove tracking event from poll() (bug 918877)
Update Russian L10n
[IT] Localized reamining strings. Thanks to Sara
Merge pull request #296 from unghost/sep21_ru

Update Russian L10n
Merge pull request #297 from gialloporpora/master

[IT] Localized new strings. Thanks to Sara
Increase default font-size by 1px (bug 918766)
Merge pull request #298 from muffinresearch/bump-fontsize-918766

Increase default font-size by 1px (bug 918766)
catch connection error (bug 884855)
Merge pull request #300 from andymckay/884855

catch connection error (bug 884855)
fatal Bango/solitude err -> sentry (bug 921249)
Turning string errors into constant ones (bug 818972)

DO NOT MERGE: it requires the solitude counterpart!
Merge pull request #299 from davidbgk/818972-error-constants

Turning string errors into constant ones (bug 818972)
restrict bounce to mozpay urls (bug 920966)
Merge pull request #302 from wraithan/restrict_bounce

restrict bounce to mozpay urls (bug 920966)
Abstract full-screen errors and add timeout to persona login (bug 870432)
Merge pull request #301 from muffinresearch/timeout-persona

Abstract full-screen errors and add timeout to persona login (bug 870432)