Bug 948858 - [UITest][HW] modify radio test for multi-SIM card device
Bug 948847 - [Gaia] add AirplaneModeHelper

- other apps can use AirplaneModeHelper to know current airplane status
- add a lot of related unit tests
- add two mozSettings key for airplane mode use
Merge pull request #15191 from MBRSL/bug-948858-multiSIM

Bug 948858 - [UITest][HW] modify radio test for multi-SIM card device, r=gasolin
Merge pull request #14836 from EragonJ/bug-948847

Bug 948847 - [Gaia] add AirplaneModeHelper to make sure settings app and system app will not do the same thing