Simplify registration of Android Installations

Remove `Installation` & `InstallationRepository`, as these classes
should mirror the remotable methods available on server models and
they don't fit the registration workflow.

Introduce a new class `LocalInstallation` that provides everything to
help LB applications with registering the Installation on the server.

Improve unit tests to use a mocked context, which allows to supply
custom version numbers.
Add timeZone & subscriptions to LocalInstallation
Merge pull request #19 from strongloop/feature/revamped-installation-model

Simplify registration of Android Installations