First try at updating to sbt-android 0.7
Added workaround for missing android.jar

as suggested by Matthew Willis on scala-on-android mailing list.
forgot to add common to aggregate
more fixes, entry class must be kept explicitly, so files go to lib, jar to libs
external jar files need to be in libs
update README
not needed in repo
part of fix from android-plugin/#189
Drop instrumentation tests

because they are broken and not essential for LibGDX applications, which are
single-window by design. Instrumentation tests is more useful for testing
Activities and such, which we do not normally use for gdx apps.
update sbt-assembly dependency
force SBT 0.12.4, because sbt-android 0.7 is not ready for SBT 0.13
Merge pull request #37 from aginiewicz/sbtandroid-0.7.x-no-tests

Sbtandroid 0.7, no instrumentation tests