[BREAKING] - Refactor NimBLEHIDDevice

* General code cleanup.
* All functions that return a characteristic or service have been renamed to have a `get` prefix to better represent their function.
* All functions that set a value have been renamed with the prefix `set` to better represent their functionality.
* Added an `bool notify` parameter to `setBatteryLevel`, which if `true`, will send a notification of the value to the peer.

Author: h2zero