provide API for bonding

[TorstenRobitzki]

As bonds are stored persistent, Bluetoe can not store them but has to provide an API to store and retrieve bonding information. Following information must be stored / retrieved:

• Peripheral MAC address
• Central MAC address
• Long Term Key
• Identity Resolution Key
• State of CCCDs
• Optional: The last notified / indicated value of characteristics with CCCD
• Method used to exchange LTKs (MITM protected, LESC, none...)
• What else?

The API might require a template, where the Bluetoe could provide certain, compile time known values, like the number of CCCDs, etc.