Bug 925278 - Make firefox/channel page localizable
* enclose strings in l10n calls + add l10n comments
* remove chevrons that are for decoration and cause l10n problems and generate them via CSS (gecko will revert them automatically in rtl)
Merge pull request #1296 from pascalchevrel/Bug-925278_Make_firefox-channel_localizable

Bug 925278 - Make firefox/channel page localizable