Slow Network Connection -- Improve Error Handling

[goodanchorage]

Double-clicking on a slow connection may result it "Unable to connect: Unknown error. (Error 1, HTTP 0)". Verify and improve error message.

Slow connection causes OpenCPN hang- with "(Not Responding)". Set up another download thread, while also showing a status/spinning wheal/"Downloading..." message?

[rgleason]

Will compile sgain in two days for win. No computer mow.

[goodanchorage]

boat_alexandra noticed this issue as well:

"If I am not connected to the internet and I click on the toolbar goodanchorage icon, opencpn gets forever stuck on goodanchorage_pi.cpp:393. It needs to give up after so long, but also this routine should really really be done in a background thread, and the toolbar icon changed to indicate it is connecting to the server."

[goodanchorage]

Jeff B reports: If the plugin is on and working (green anchor), followed by turning off internet connection, any attempt to right click on a new marker to get info hangs the app.