Support for Unit and Performance Testing (Desktop and Android) and Instrumentation Testing (Android)

Testing frameworks are very important for my style of working, and I believe everyone can benefit from some unit or instrumentation tests. I've used those features in jberkel/android-app.g8 and missed it from this template. Those 4 commits are a try to bring in slightly simplified version of those in.

The biggest change is probably adding "all-platforms" aggregated target. That way, we can compile or test all platforms at once by issuing single "test" sbt command. Instrumentation testing is little harder, but it uses commands from android-plugin so is quite standard. Used android-tests for it to underline, that it is android based.

If someone does not need tests, this does not change much - one can just ignore those then and use everything like it was. Library dependencies are added only when test is used (it has % test as qualifier).

I also provided one (pending) unit test in common, and one actual test in Instrumentation test as examples.

Since last edit, this also includes ScalaMeter (which is very useful, but hard to get right on JDK6).