Add feature: remove service (#17)

* Get service handles on server start

* remove service + indicate service changed

* Reset gatt services when no connections active and services changed.

* NimBLEServer::createService can now be used any time and will send service changed
indication if server was already active.

* Add ability to remove advertised serviceUUIDS

* Adds addService() method to server to be allow user to re-add a service previously removed

* Add destructior to NimBLEServer, NimBLEService and NimBLECharacteristic to release allocated resources.

src/NimBLECharacteristic.cpp

@@ -58,6 +58,9 @@ NimBLECharacteristic::NimBLECharacteristic(const NimBLEUUID &uuid, uint16_t prop
  * @brief Destructor.
  */
 NimBLECharacteristic::~NimBLECharacteristic() {
+    for(auto &it : m_dscVec) {
+        delete it;
+    }
 } // ~NimBLECharacteristic