Connection state - master role

Hello !

Here is my implementation of the connected state in Master role. 
The provided example works for me in communication with a custom nRF51822 device (using Nordic S110). This device implements the Battery Service and a custom service that controls a LED via PWM, which allows to test data TX & RX.

I saw that you pushed quite a lot of commits since I wrote this, so I think I will have to work again on the events and callback part... Using the brand new `ll_plat` API ?