Set stalker extension defaults for android projects.

Stalker extension defaults are set for android projects that use android plugin
0.9.+. This version was chosen because the DSL for Library Projects is the
same as for application projects. Supporting older android plugin versions
would require a little more complexity.

* Update sample android projects to use android plugin 0.9.0 and remove stalker
configuration.
* Add tests.
Update .travis.yml

Configure Travis CI to install necessary Android SDK dependencies
Configure only a single environment build
Inline exports in .travis.yml
Fix PATH in .travis.yml
Remove gradlew installation

- gradlew is already included in the repo
Merge pull request #26 from VandalSoftware/set-defaults

Set stalker extension defaults for android projects.