fix #21,#52 added Unit Tests for org.scaloid.common.app with Robolectric and ScalaTest

Please let me send PR of Unit Test, which is implemented in Robolectric and ScalaTest.

Since it's the first time to send PR to your repository, I've implemented tests only for org.scaloid.common.app . If it's no problem, I'm thinking to implement tests for other parts as well.

Would you please merge this PR if it's OK for you?
If any, please feel free to let me know.

Thanks!