Register receiver for TIMEZONE_CHANGED broadcasts at runtime only.

As the timezone changed receiver is registered in the library manifest, a new process is started to run the receiver if the application isn't already running. Since timezone changes would be a rare event for most users it probably doesn't matter, but I thought it would be neater to avoid this.

This change registers the receiver as part of init instead of in the manifest, so it will only be triggered if the application process is still running when a time zone change occurs.

I've added a JodaTimeAndroid utility class with a static init method to initialize both ResourceZoneInfoProvider and register the broadcast receiver, for lack of a better idea of where it could go.

Do you think this change is worth adding?