improved wifi initial connection - especially if station wifi is not available #509
removed new operators from web.h (reduce dynamic allocation)
improved sun calculation #515, #505
fixed wifi auto reconnect #509
added disable night communication flag to MQTT #505
changed MQTT publish of `available` and `available_text` to sunset #468
added icons to index.html, added wifi-strength symbol on each page
moved packet stats and sun to system.html
refactored communication offset (adjustable in minutes now)