BLE fixes 2020 1

Just two random fixes.

• Introduce cccd.h which will make it easier to introduce new characteristics with notification support
• Prevent redundant writing of pairing information each time a device disconnects

Looks good to me! Thanks for keeping our codebase clean.

However, I'm only a bot - so a human will still have to approve this request.

merged

mentioned in commit f79bd076

<3