[ios] - add support for bluetooth keyboard

This implements basic support of BT Keyboard for iOS. Since there is no real direct access via public APIS we do the following:

1. Implement the UIKeyInput protocol for receiving all "normal" keys including return and backspace. This gives us nearly all keys of a generic bt keyboard but its lacking the cursor keys
2. Override the sendEvent method in UIApplication for catching the cursor keys. Yeah its really hacked. But i found this approach somewhere in the net and it works. There is no other way for getting those events. I decided to not implement the whole keyboard via this hack because if this breaks somewhen - we at leat keep all the other keys ;)

There is no way for handling the ESC key though. This key acts as home button and is not send via one of those 2 approaches.

Comments requested from @davilla and @ulion.