Restructuring project

Sources now go into following folders:
/sources
/common
/android
/ios

Project files are contained in build folder:
/build
/android
/ios

iOS project file and corresponding code from Sachs hasn't made its way
into the repository yet.

Next step - migrate android to gradle build system.
Android.mk for new project structure and typo fix

Fixed missing bracket in BasicActivity.java (what a shame!).
Android.mk now corresponds new project structure.