Borderless window mode is the only window mode.

Also fix bugs resulting from removal of WinForms config editor, which
will soon be replaced with a prettier WPF config editor.

startMaximized and noBorder config options removed,
As a borderless window is now the only windowed mode available due to
System.Windows.Shell.WindowChrome making it superior in aesthetics than
with windowchrome as well as more practical than with borderless
behaviour in legacy. As such, startMaximized has been removed due to the
absence of a windowed mode with a border, a borderless maximized window
is similar if not identical in effect to fullscreenMode.

CheckBattlelogiumConnection has been rewritten to be faster,
CheckBattlelogConnection() in UICore has been fixed and made async.

Also fix tiny error in config.ini, we use semicolons for comments
following standard .ini format rather than double slashes.