m2e-android compatibility

This commit adds the project.properties file and marks the
maven-android-plugin goal consume-aar ignored in m2e build. The project
now can be imported into eclipse and the tests can be run without any
further config using the m2e-android plugin.
Use Travis Android language support.

Closes #16.
Removed consume-aar ignore in m2e from pom

consume-aar lifecycle mapping removed from pom, because it would make
users think aars are built into the apk in Eclipse build, but they are
not. Also added some information about this in readme.
Merge pull request #15 from WonderCsabo/m2e-android_compatibility

m2e-android compatibility
Upgrade the versions of robolectric and android-maven-plugin.
Upgrade robolectric to version 2.4-SNAPSHOT.