Revert "Bug 946556 - [Music] Disable the play controls when using a bluetooth headset in a call"

This reverts commit a69025bfe657a07cca372369e0d4b83a442fba73.
Merge pull request #16020 from dominickuo/revert-bug-946556

Revert "Bug 946556 - [Music] Disable the play controls when using a bluetooth headset in a call
Bug 966951 - "Group Call" is inactive when received call is hung up
Merge pull request #15955 from Rik/inactive-group-after-finishing-call-966951

Bug 966951 - "Group Call" is inactive when received call is hung up r=etienne
Fix a syntax error in one .properties file
Initialize mozL10n in webapp-optimize
Fix Gallery tests
Refactor l10n.js