Refactor NimBLEExtAdvertising

* General code cleanup
* `NimBLEExtAdvertisement` : All functions that set data now return `bool`, true = success.
* Added new method, `NimBLEExtAdvertisement::removeData`, which will remove the data of the specified type from the advertisement.
* Added new method, `NimBLEExtAdvertisement::addServiceUUID`, which will append to the service uuids advertised.
* Added new method, `NimBLEExtAdvertisement::removeServiceUUID`, which will remove the service from the uuids advertised.
* Added new method, `NimBLEExtAdvertisement::removeServices`, which will remove all service uuids advertised.
* Added overloads for `NimBLEExtAdvertisement::setServiceData` with the parameters `const NimBLEUUID& uuid, const uint8_t* data, size_t length` and
  `const NimBLEUUID& uuid, const std::vector<uint8_t>& data`.
* Added new method, `NimBLEExtAdvertisement::getDataLocation`, which returns the location in the advertisment data of the type requested in parameter `uint8_t type`.
* Added new method, `toString` which returns a Hex string representation of the advertisement data.