1.0 beta 2

1. Fix a potential crash in Search
2. Update the interaction in Favorite-Bookmarks
3. Load Celestia library asynchronously on start up
4. Display tutorial message on first start up
5. Support reading extras directory (for add-ons), it should be located in Android/data/space.celestia.mobilecelestia/files/CelestiaResources/extras
6. In APK, a crash reporting system (App Center) is incorporated