Big refactoring

First of all I'm sorry that I made this all in one commit :worried:

I still what to make some changes so consider this work in progress.

This is a big refactoring containing:

- organize files in packages

- renaming of id's, classes, variables, methods etc.

- breaking up of classes and methods so that they have less / only one responsibility

- adding of Java beans as data model

- definition of the streams in xml files instead of code

- moving large text to files instead of code

- removing duplicate code

- adding radio streams which will be played in the video player (just for now, should be changed)

- adding a copyright and license notice to every file: should it be copyrighted by Gospel Ministries International or do you what it by individuals?

- improvements to the build script

- update `README` to add badges to Google Play and Travis CI

- I guess many other changes I can't remember now :smile:

Although this is not yet ready for merging, I pushed it here so you could have a look. Will push further changes in a couple of days.