Reflection-less Index generation [Upto 70% improvement in performance]

[yasirmhd]

While generating the Subscriber indices there is an opportunity to do away with reflection.

Using the interface SubscriberMethodInvoker anonymous classes are generated which access the public methods of the class directly.

Older implementation :

New Implementation :

[yasirmhd]

@greenrobot-team : The build seems to be failing with 1 lint issue though it passes for me. We have tried to fix the build breakage on the master here with these fixes as well. We do not have access to the travis logs for lint warnings for us to be able to action it.