Build APK via Travis

* Only tries to build and deploy on non-forks
    * Feedback time for tests is maintained

* Two build types: "snapshots" and "releases"
    * If commit contains a `git tag`, it's considered a release
    * If release, produce a signed build

* If non-fork, try to deploy to S3
    * S3 is public-readable and can be browsed using [Shrub][]
    * Flowdock notified via [RSS][]

* Use `grunt release` to bump the package version *as well as* the Android version code, see 2615111.

[shrub]: https://shrub.appspot.com/eha-lomis/
[rss]: https://shrub.appspot.com/eha-lomis/?format=rss