Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/6e8bf8702419
Author: punamdahiya <punamdahiya@yahoo.com>
Desc: Merge pull request #16967 from punamdahiya/Bug976481

Bug 976481: remove the useless and buggy Media Storage Settings button from the media apps

========

https://hg.mozilla.org/integration/gaia-central/rev/c72a5a218f68
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 976481: remove the useless and buggy Media Storage Settings button
from the media apps and update the text displayed when there is no sdcard.
Also ensure that all media apps have a cancel button if invoked for a pick
activity when there is no sdcard.

remove storage setting button and update dialog text for Gallery app

modify the nocard message in the Video app

Remove storage settings button from Music app overlay, change overlay message, and add a Cancel button for pick activities

Remove unused string from Gallery locale file

Remove unused string from Video locale file

Remove the storage settings button and text from the Camera overlay
Bumping manifests a=b2g-bump