* NimBLEClient::disconnect() was setting the connected flag to false before the disconnection occured.
* NimBLEDevice::deleteClient() was not waiting for disconnection if it was already in progress.
* Client gap event handler was releasing the connection event semaphore when it should not.
* Add NimBLERemoteCharacteristic::getValue(time_t *timestamp = nullptr) to get the latest remote characteristic and (optionally) it's timestamp.
* Added a timestamp to NimBLEAdvertisedDevice for the moment a device was scanned
Previously we used createServer() to get a reference to the server instance.
This was problematic when using advertising only as it would create a server
when starting advertising. This prevents that and provides better semantics.
This allows NimBLE options in menuconfig to reduce code size based on
the roles selected (scan/advertising/central/peripheral).
Significant code space can be saved by removing unnecessary roles for the application.
