Add new APIs to GAP bond manager: read and write bonding records to and in SNV.

• Add new APIs:
  • gapBondMgrReadBondRec - Read bond record from the NV
  • gapBondMgrImportBond - Saves external bond record to the NV
    Both functions are public and defined in gapbondmgr.h

• Move the following items from gapbondmgr.c to gapbondmgr.h to make them publically accessible:
  • #define GAP_BOND_REC_ID_OFFSET
  • #define GAP_BOND_LOCAL_LTK_OFFSET
  • #define GAP_BOND_DEV_LTK_OFFSET
  • #define GAP_BOND_DEV_IRK_OFFSET
  • #define GAP_BOND_DEV_CSRK_OFFSET
  • #define GAP_BOND_DEV_SIGN_COUNTER_OFFSET
  • #define GAP_BOND_REC_IDS
  • #define GAP_BONDED_STATE_AUTHENTICATED
  • #define GAP_BONDED_STATE_SERVICE_CHANGED
  • #define GAP_BONDED_STATE_CAR
  • #define GAP_BONDED_STATE_SECURECONNECTION
  • #define GAP_BONDED_STATE_RPA_ONLY
  • typedef struct {...} gapBondLTK_t;
  • typedef struct {...} gapBondRec_t;
  • typedef struct {...} gapBondCharCfg_t;