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
Merge pull request #4520 from ScottNZ/new-menu

Unify ra and cnc main menu logic
Tidy AutoTarget code.
Remove redundant AttackMove definitions.
Add AttackMove support to RA aircraft.
Simplify HeliFly interface.
Add range support to HeliFly.
Simplify Fly interface.
Add range support to Fly.
Ensure that planes circle after being ordered via IMove.
Add following to IMove.
Add Guard support to Aircraft.
Fix HeliFly lua bindings.
Make aircraft guardable.