Updated rubyzip dependency, and removed xamarin-test-cloud dependency.

Updated `rubyzip` dependency, so that we use a more recent version. `rubyzip` 1.0 breaks the interface, so (simple) code changes were required.

I've successfully uploaded a test with the locally built `calabash-android` gem, rebuilt a test server, etc., so it seems like everything's OK.

There's a slight complication: `calabash-android` depended on the `xamarin-test-cloud` gem, which again depends (currently) on `rubyzip` 0.9.9. I agreed with @krukow that the best solution is to remove the dependency from `calabash-android` to `xamarin-test-cloud`, and then create a new gem, simply called `calabash`, which depends on `calabash-android`, `calabash-cucumber` (a.k.a. calabash-ios), and `xamarin-test-cloud`. We'll also update the `xamarin-test-cloud` gem to use a newer `rubyzip`.

@TobiasRoikjer or @jonasmaturana will you please have a look at this PR and merge if it looks OK to you? I think you should be in the loop. After `calabash-android` 0.5.0 is released, we'll release an updated `xamarin-test-cloud` gem.