Pitfall when using Hockey-UpdateActivity and different Buildtypes

[Plinzen]

Currently the Hockey-UpdateActivity has been moved to debug-Buildtype. This could cause an issue in Crashtracker-class:

final boolean shouldShowUpdates = BuildConfig.DEBUG && !BuildConfig.IS_IDE_BUILD;
  final boolean isUpdateActivity = !activity.getClass().equals(UpdateActivity.class);
  if (shouldShowUpdates && isUpdateActivity) {
     UpdateManager.register(activity, application.getString(R.string.hockey_app_id));
  }
}

The statement to register this activity for the UpdateManager depends on the BuildConfig.DEBUG-attribute, which has no direct dependency to debug-Buildtype (it is set by the debuggable-flag in build.gradle). If we create a new BuildType which has this debuggable-flag set to true, we also have to add the Hockey-UpdateActivity to the Manifest of this newly created BuildType. This could be a pitfall, because it could easily be forgotten and is not recognized by the developer if the app was build via IDE, currently. If the entry is forgotten in the Manifest, the app will crash when trying to open the Hockey-UpdateActivity.

This issue has a reference to this PR: #20