JNI: Initial commit of Java library + example program

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Enable JNI in build

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Add libstoken to build

This was tested with NDK release r8e on ARM (on a real device) and
x86 (compile only).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>