New command to preload Scala on a device/emulator

Here is a new command to quickly setup your device (or emulator) for Scala development.

It predexes the Scala libs then pushes them to the device, most of it being heavily inspired by svenwiegand/scala-libs-for-android-emulator. These are the two main commands you can use :

  * `android:preload-device`
  * `android:unload-device`

I tested it on my device (Galaxy Nexus running Cyanogen 10.1-M2) and it apparently runs flawlessly.