add twitter app dev credentials

[vdaubry]

We really need to do something about security, having our twitter app credentials publicly on github is a terrible thing...

I'll have a look at how buffer handles the twitter auth : https://github.com/bufferapp/buffer-chrome

[tibo]

Ok my bad, I didn't pushed my latests changes with the right URL.
I still have few things to do on this (error handling, design of thte interface...)
I will merge this once it's done.