nrf51288-DK BLE peripheral security

Thanks - this looks good. Yes, I think letting the softdevice handle permissions is definitely a really nice addition.

The write causing bonding to initiate definitely seems what I'd expect based on how I've seen other devices working.

Your branch looks great as well - although it might be good to add a check for readVar!=NULL and same for writeVar (maybe just in set_security_mode?). I'm pretty sure this'll work with what you've done, but it'd be nice if you could do just something like:

security: {  write: {  encrypted: true } },

as a shorthand - so you don't have to mention everything.