Make application using library import only a single module

[mcomella]

Currently, we have the user download the primary module and its dependencies (something like):

    compile(group: 'org.mozilla.sync', name: 'accounts', version: '0.0.1', ext: 'aar', classifier: '')
    compile(group: 'org.mozilla.sync', name: 'fennec', version: '0.0.1', ext: 'aar', classifier: '')
    compile(group: 'org.mozilla.sync', name: 'thirdparty', version: '0.0.1', ext: 'aar', classifier: '')

This is a side-effect to the way we publish resources because I couldn't figure out the right way (for more details, see ./publish.gradle). Instead, we want:

    compile 'org.mozilla.sync:accounts:0.0.1'

Ideally, we also ensure the dependencies are not visible to the application using our library. This works when the dependency is external (e.g. adding picasso to the accounts/ module will not expose it to the application) so it should be possible.