Bug 963917: reduce Gallery memory use (and fix leak) while scanning

force software canvases for thumbnail and preview creation with willReadFrequently

Free canvas memory after creating a thumbnail

Make sure our thumbnail blobs are file-backed not memory-backed

update mediadb docs
(cherry picked from commit 4b5eaa4a2823d8961b80a3b975b1eeed92b9fcb7)

Conflicts:

	apps/gallery/js/MetadataParser.js
	apps/gallery/js/gallery.js
Bug 952797 - Reactivation the dialer keypad integrations tests.
(the marionette issue was fixed by bug 891882)
Bug 930563 - [B2G][L10n][Clock] Chinese Traditional: Highlight date instead of first number displayed.
Bug 960705 - [clock][l10n] Close button should say Stop instead; r=reviews
Bug 955626 - Change start_b2g wait in GaiaTest to wait for AppWindowManager to acknowledge the active frame instead of js event
Bug 971691 - "day view header copy should not overflow" marionette js test is failing
Merge pull request #16214 from millermedeiros/971691-travis-day-view-header

Bug 971691 - "day view header copy should not overflow" marionette js test is failing r=gaye
Bug 970879 - Prevent redundant listeners from being registered during testing r=julienw

- Refactored the WapPushManager object to not use bound functions for
  event listeners
- Modified the unit-tests to improve control over the document visibility
Bug 971761 - Enable requestWakeLock in DEBUG builds to turn our tests green
Bug 962040 - blacklist camera until we figure out why it hangs.
Merge pull request #16219 from Rik/wakelock-enabled-971761

Bug 971761 - Enable requestWakeLock in DEBUG builds to turn our tests gr... r=kgrandon
Bug 970422 - Drop z-index of messages to go under the scrollbar. r=julien
Merge pull request #16173 from etiennesegonzac/bug-952797-reactivating-dialer-keypad-integration

Bug 952797 - Reactivating the dialer keypad integrations tests. r=rik
Merge pull request #16208 from gabrielesvelto/bug-970879-prevent-redundant-listeners

Bug 970879 - Prevent redundant listeners from being registered during testing r=julienw
Bug 968220 - Add a "Developer HUD" sub-menu in "Developer". r=vingtetun
Merge pull request #16092 from hfiguiere/bug962040-2

Bug 962040 - blacklist camera until we figure out why it hangs. r=julienw
Bug 964918 - Fix timing in Python test_kill_multiple r=me a=testonly
Merge pull request #14991 from zacc/bug_955626

Bug 955626 - Change wait in GaiaTest class to wait for AppWindowManager ...
Merge pull request #16091 from jankeromnes/developerhud

Bug 968220 - Add a "Developer HUD" sub-menu in "Developer". r=vingtetun

Note that this also deletes the Grid overlay.
Bug 969587 - Make customization run without ICCHelper present