Minor details and useless functionalities

[Sartharian]

1. The IResponseListener's interface implementation does not contain a definition for state codes like IBLEWriteResponse's implementation does with Code.toString()
   Please edit the docs for make suggested use of "Constants" instead of "int"

2. The only way to determine if the paired device is connected is by calling getCurrentDeviceAddress(String mac).
   isCurrentDeviceConnected() also isDeviceConnected() are both useless (return false anyways).

3. NullPointerException after FindDeviceByPhone's onDevFounded caller interface was invoked (to check if the device is founded by user is impossible if the caller interface instance is never setted on library ).
   (i'm getting the stacktrace, will edit soon)

Cheers & happy coding!