GPII-900: Improving Grunt build utilities

Still missing a few details, but within this we are able to perform the same actions
as from using android-gpii.sh script.

Adding global tasks:
 * checkBuildEnv
 * buildApk
 * buildTarGz
 * build
 * install
 * installPrivilegedApk

Also, adding some shell subtasks:
 * buildApk
 * copyToBuildFolder
 * createAndroidTarGz
 * installJs
 * installApk
 * installPrivilegedApk