Some maintenance changes.

- Fix a copy/paste error in the comments for a version boolean in AppData.java
- Some instance variables can be final in MultiSelectListPreference.java
- Some instance variables can be final in PathPreference.java. This also allows for removal of a null check, as the variable being tested cannot be null (as it was made final).
- Replaced a .equals test for emptiness of a string with !TextUtils.isEmpty()