Allow features to be disabled at build time (#143)

* Add framework for built-time feature selection
* Allow MQTT, NTP, OTA features to be disabled at build time
* Allow Project screens to be disabled at build time
* Allow security features to be disabled at build time
* Switch to std::function for StatefulService function aliases for greater flexibility
* Bump various UI lib versions
* Update docs

interface/src/api/Endpoints.ts

@@ -1,5 +1,6 @@
 import { ENDPOINT_ROOT } from './Env';
 
+export const FEATURES_ENDPOINT = ENDPOINT_ROOT + "features";
 export const NTP_STATUS_ENDPOINT = ENDPOINT_ROOT + "ntpStatus";
 export const NTP_SETTINGS_ENDPOINT = ENDPOINT_ROOT + "ntpSettings";
 export const AP_SETTINGS_ENDPOINT = ENDPOINT_ROOT + "apSettings";