Merge pull request #18201 from etiennesegonzac/instacallscreen

Bug 990003 - Introducing a dedicated callscreen app for better performance r=rik, alive, 21
(cherry picked from commit 7afce8a6e965a45f38988227828ccdfb315394f3)

Conflicts:
	apps/communications/dialer/js/call_log.js
	apps/system/js/attention_screen.js
	apps/system/js/bootstrap.js
	apps/system/style/attention_screen.css
	apps/system/test/unit/bootstrap_test.js
	build/csslint/xfail.list
	build/jshint/xfail.list
	build/webapp-zip.js
Merge pull request #18521 from etiennesegonzac/bug-997924-callscreen-fix-visibility

Bug 997924 - Make sure the preloaded callscreen doesn't keep an audio channel open
(cherry picked from commit c0e3264cf1e57d2da3ce201554b620bd3cf01d24)
Merge pull request #18537 from Rik/settings-readwrite-999545

Bug 999545 - Callscreen app needs write access to settings r=etienne
(cherry picked from commit 69c41df810a1304ee9bab956468c391472f0f792)
Merge pull request #18694 from etiennesegonzac/bug-1000047-callscreen-race

Bug 1000047 - Hardening the callscreen against a transition end race. r=rik
(cherry picked from commit d9cb98243113558e4581c6bfcb6515ae6b088620)
Merge pull request #18577 from etiennesegonzac/bug-999478-on-demand-callscreen

Bug 999478 - Free the preloaded callscreen under memory pressure
(cherry picked from commit 03da6aab8a033d83835a245c968ce4dd2f06409e)
Merge pull request #19070 from lissyx/bug1006356

Bug 1006356 - Fix setting currentChannel value r=etienne_s,rik
(cherry picked from commit 78a31887c15d26f38df0e86c3f799c0c08d4b81b)
Merge pull request #21282 from etiennesegonzac/callscreen-1.4-uplift

Callscreen 1.4 uplift