* [BT] Add BM2 voltage
Voltage retrieval through a BLE connection, frequency of the BLE connection is defined by `intervalcnct`
* Add doc
Credits to https://github.com/KrystianD/bm2-battery-monitor
* Use a task to process immediate BLE actions to prevent MQTT disconnection if the action takes too long to complete.
* Add state_on and state_off parameters to createDiscovery
* Add immediate parameter to BLE connection commands.
When sending a command to read/write a characteristic on a BLE server this adds a new parameter to cause the action to be
performed immediately. This will stop the scan in progress to perform the actions queued.
Example use:
```
mosquitto_pub -t home/OpenMQTTGateway/commands/MQTTtoBT/config -m '{
"ble_write_address":"AA:BB:CC:DD:EE:FF",
"ble_write_service":"cba20d00-224d-11e6-9fb8-0002a5d5c51b",
"ble_write_char":"cba20002-224d-11e6-9fb8-0002a5d5c51b",
"ble_write_value":"TEST",
"value_type":"STRING",
"ttl":4,
"immediate":true }'
```
Stop BLE processing when immeditate command sent.
* Use a shorter connection timeout.
* Update docs.
* Remove MQTT spam for connection retrys
* Prevent crashing when the normal connection process occurs at the same time as an immediate action.
* Use a semaphore to protect BLE device vector.
* EXPERIMENTAL: Ble read/write characteristics over MQTT.
Uses #979
This allows reading and writing BLE characteristics from an MQTT message.
Example format:
mosquitto_pub -t home/OpenMQTTGateway/commands/MQTTtoBT/config -m '{"ble_write_address":"AA:BB:CC:DD:EE:FF", "ble_write_service":"cba20d00-224d-11e6-9fb8-0002a5d5c51b", "ble_write_char":"cba20002-224d-11e6-9fb8-0002a5d5c51b", "ble_write_value":"TEST", "ttl":4 }'
mosquitto_pub -t home/OpenMQTTGateway/commands/MQTTtoBT/config -m '{"ble_read_address":"30:AE:A4:7C:3C:A6", "ble_read_service":"cba20d00-224d-11e6-9fb8-0002a5d5c51b", "ble_read_char":"cba20002-224d-11e6-9fb8-0002a5d5c51b", "ttl": 2 }'
The ttl parameter is the number of calls to connect (defaults to 1), which occur after the BLE scan completes.
A response is provided over MQTT in the format:
write : {"id":"30:AE:A4:7C:3C:A6","service":"cba20d00-224d-11e6-9fb8-0002a5d5c51b","characteristic":"cba20002-224d-11e6-9fb8-0002a5d5c51b","write":"TEST","success":true}
read : {"id":"30:AE:A4:7C:3C:A6","service":"cba20d00-224d-11e6-9fb8-0002a5d5c51b","characteristic":"cba20002-224d-11e6-9fb8-0002a5d5c51b","read":"TEST","success":true}
* Add generic BLE connect class and read data as hex.
* Add value_type parameter and document usage
* Add note to docs
