Travis CI builds

* Added .travis.yml that does the following:
  * creates an avd
  * starts an emulator
  * waits for the emulator to start
  * sets up the android sdk and the required components (with the needed license)
  * builds the source code
  * uploads the built artifact (apk) to github releases (only if a git tag was created for the same)
updating the github encrypted key
Merge branch 'travis_builds'
update travis.yml for nightscout's repo
adding @jasoncalabrese's encrypted secret
Merge pull request #20 from virmani/master

Setting up travis builds