Fixed #45

* extracted about fragment
* added open source note
* simplified about screen
* restructured license notes
Extracted some Exceptions and OpencorePlayerProfilingInfo.java
Using DummyPlayerCallback instead of null check
Merged break conditions
executed "reformat" and "optimize imports"
Extreacted some Exceptions and OpencorePlayerProfilingInfo.java
Some minor refactorings and documentations
Some build tool changes

* 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
Fixed travis build
Added English translation
Moved all untranslateable strings to one place
Fixed some translations; fixed #70