Ble read/write characteristics over MQTT. (#988)

* 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

main/ZgatewayBLEConnect.h

@@ -4,6 +4,7 @@
 #ifdef ESP32
 #  include "ArduinoJson.h"
 #  include "NimBLEDevice.h"
+#  include "config_BT.h"
 
 extern void pubBT(JsonObject& data);
 
@@ -13,6 +14,9 @@ public:
   TaskHandle_t m_taskHandle = nullptr;
   zBLEConnect(NimBLEAddress& addr) { m_pClient = NimBLEDevice::createClient(addr); }
   virtual ~zBLEConnect() { NimBLEDevice::deleteClient(m_pClient); }
+  virtual bool writeData(BLEAction* action);
+  virtual bool readData(BLEAction* action);
+  virtual bool processActions(std::vector<BLEAction>& actions);
   virtual void publishData() {}
   virtual NimBLERemoteCharacteristic* getCharacteristic(const NimBLEUUID& service, const NimBLEUUID& characteristic);
 };
@@ -34,5 +38,12 @@ public:
   void publishData() override;
 };
 
+class GENERIC_connect : public zBLEConnect {
+  std::vector<uint8_t> m_data;
+
+public:
+  GENERIC_connect(NimBLEAddress& addr) : zBLEConnect(addr) {}
+};
+
 #endif //ESP32
 #endif //zBLEConnect_h