This patch adds independent management of security requirement for read, write and update operatiosn of a GattCharacteristic.
Requirements are defined after ble::att_security_requirement_t that maps LE security mode 1 and LE security mode 2.
The functions requireSecurity and getRequiredSecurity are deprecated as SecurityManager::ScurityMode_t does not map well with LE security modes.
In the process, the path has been shortened and the unecessary ble
directory between FEATURE_BLE and the actual implementation has been
removed.
commit id of ARMmbed : 17728a824c7273e16b6b74fae871e2997c88ecd1