Feature service

[rjwats]

A feature availability service would allow us to turn on and off features at build time and omit them from the binary using #defines - hiding them in the UI dynamically.

The idea here is that features would register themselves when constructed. The UI would build a "FeatureContext" from an initial request to the server to discover which features are available.

This will enable the framework to support more features without burdening users with features they won't use, some examples:

• OTA Updates
• NTP
• Authentication/User Management
• MQTT
• Serial/Telnet Terminal