Refactor code to allow for configuration

[forfuncsake]

These items (and probably more) need to be configurable:

On ESP8266:

• WiFi credentials
• API credentials (enabled/disabled and values)
• Whether to use one or two sensors, if only one, detect open or closed?
• HomeKit proxy refresh URL
• Whether to pingback to HK proxy at all
• Button hold time
• Door transition time

In proxy:

• API URL
• API credentials
• hc db file location
• HTTP server port
• Info struct values (name, serial, etc)
• HomeKit setup PIN
• API guard time

[forfuncsake]

Proxy part of this has been addressed by 0f14427