Bug 1098239 - Rewrite mobile/android Gradle integration. r=me

This is a big patch, but it's essentially NPOTB.  The part that is POTB
is ... removing Gradle integration from the build.  I've implemented
|mach gradle-install| as a substitute for the build system stuff; it's
just so much easier to iterate on a mach command than a moz.build and
Makefile.in.

I'm landing this with self-review because this lessens the impact of the
Gradle integration on the build system and because I am the only person
who understands either the old or the new system.

You'll need to run |mach gradle-install| at top level to configure the
new Gradle integration.  But |mach gradle ...| does the right thing
configuration steps too.

This patch rewrites most of the Gradle integration.  The major changes
are:

* all .gradle files move into mobile/android/gradle;
* all the Gradle projects live in the object directory;
* mozconfig exposed to all build.gradle files;
* simplification of Android configuration between build.gradle files;
* support for user-specified version of build tools;
* first steps towards supporting builds from the source directory;
* bumps Gradle to 2.2.1;
* bumps the Android-Gradle plugin to 0.14.4.

This is seemingly a step backwards given that we'd prefer to ship the
.idea directory in the source directory.  But in fact we get closer to
that; it's possible to run ./gradlew in the source directory and get a
reasonable build.  We'll progress with this in time.  The win right now
is that the projects are nested, which makes importing work better on
Linux machines.

Unfortunately IntelliJ 13 and 14 now have conflicting Android-Gradle
plugin version requirements, so we now only support IntelliJ 14.0.2 and
above.

--HG--
rename : mobile/android/base/gradle_AndroidManifest.xml => mobile/android/gradle/base/AndroidManifest.xml
rename : mobile/android/base/gradle_AndroidManifest.xml => mobile/android/gradle/branding/AndroidManifest.xml
rename : mobile/android/gradle/omnijar/gradle_AndroidManifest.xml => mobile/android/gradle/omnijar/AndroidManifest.xml
rename : mobile/android/base/gradle_AndroidManifest.xml => mobile/android/gradle/preprocessed_code/AndroidManifest.xml
rename : mobile/android/base/gradle_AndroidManifest.xml => mobile/android/gradle/preprocessed_resources/AndroidManifest.xml
rename : mobile/android/thirdparty/gradle_AndroidManifest.xml => mobile/android/gradle/thirdparty/AndroidManifest.xml