Fixed #45

* extracted about fragment
* added open source note
* simplified about screen
* restructured license notes
Extracted OpenCorePlayRunnable.java
Refactored OpenCorePlayRunnable.java
Extreacted some Exceptions and OpencorePlayerProfilingInfo.java
Better Exception inheritance
Using DummyPlayerCallback instead of null check
Using new android gradle plugin and buildtools. fixed an error that was discovered via travis.
Corrected some more build script related changes
Remoed unused imports
Merge pull request #69 from ironjan/solving_too_complex_methods

Solving too complex methods