Ability to build using jitpack

[philippeauriach]

Following ustructions here : https://github.com/jitpack/jitpack.io/blob/master/ANDROID.md

This allow developers to build this lib using jitpack, without having to publish the module. Useful when working on forks. For example, this allow me to compile from my forked branch using this line in my project :
compile 'com.github.philippeauriach:ChatKit:jitpack-SNAPSHOT'

[mario]

Hello,

considering that the library is not maintained and I actively use it, I have decided to fork it for the time being under the same name. Changes to naming and other practices will come in the future.

In the mean time, I will look at your PR and consider merging it.

I hope we can revive this project together.

https://github.com/mario/chatkit

Cheers,
Mario