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)
removed wrong "inverter type can't be detected!" messages
repaired NTP and static IP #459
MQTT status about availability and produce are retain messages now
added heap as MQTT publish
updated User_Manual.md to latest changes
development build will have now always the same name because of static link from https://ahoydtu.de