This commit allows the user to set/get the GAP device name used by service
0x1800, characteristic 0x2a00. The usage is:
BLE.config(gap_name="myname")
print(BLE.config("gap_name"))
As part of this change the compile-time setting
MICROPY_PY_BLUETOOTH_DEFAULT_NAME is renamed to
MICROPY_PY_BLUETOOTH_DEFAULT_GAP_NAME to emphasise its link to GAP and this
new "gap_name" config value. And the default value of this for the NimBLE
bindings is changed from "PYBD" to "MPY NIMBLE" to be more generic.
