Follow code style guide and minor patches

Android code style guide: https://source.android.com/source/code-style.html
Java code conventions: http://www.oracle.com/technetwork/java/codeconvtoc-136057.html

Patches:
- Use ViewHolder pattern for View recycling in ListAdapter
- Make class member variables of `BGMStoreQuery` private
- Make Github TextView look like a link
- Use UTF-8 encoding
- Optimize imports
- Remove unused or unnecessary code, resources