Catch IOExceptions in Connection.cs. Closes #4083. Closes #4423.
Show an error dialog if disconnected from the server.
Update changelog.
Merge pull request #4519 from pchote/network-crash

Catch IOExceptions in Connection.cs.
Merge pull request #4523 from pchote/disconnect-dialog

Show an error dialog if disconnected from the server.
Unify ra and cnc main menu logic and clean up the main menus.
Move a bunch of buttons into an Extras submenu and the server browser.
Move CncMenuPaletteEffect to ra so it can be used elsewhere and rename it to MenuPaletteEffect.
Update CHANGELOG: add entries for new menus and reword some existing entries