Bug 1094362 - Completely disable update prefs for reftest. r=vingtetun, r=jgriffin

When running reftests on Mulet, we do not want that forced update
checking gets triggered. We can block this by setting the following
prefs:
 - app.update.enabled to false
 - app.update.url.override and app.update.url to empty string
We also disable tiles-related pinging and downloading by setting empy
values for:
 - browser.newtabpage.directory.source
 - browser.newtabpage.directory.ping
Gaia also does force check app updates at some point, so we introduce a
new pref, webapps.update.enabled, that we can use to make sure webapps
update won't be triggered.
Bug 1101334 - Part 1: Modify the MMI parser (TelephonyService.js). r=aknow
Bug 1101334 - Part 2: Modify related testcase. r=aknow
Bug 1105782 - Allow sideloading apps with unsecure permissions to the simulator. r=jryans
Bug 1107260 - Customize default screen size with a pref. r=fabrice
Bug 1107756 - Allows overloading the system apps if devtools are unrestricted. r=jryans