Make flyout menus mutually exclusive (ie. Only one flyout can be open at any one time)
Make flyout menus mutually exclusive (ie. Only one flyout can be open at any one time)

This is not 1:1 behavior with Fusion (which is more difficult to implement), but is still better than what we currently have.

Fixes #244

jumpinjackie/mapguide-react-layout,jumpinjackie/mapguide-react-layout,jumpinjackie/mapguide-react-layout,jumpinjackie/mapguide-react-layout,jumpinjackie/mapguide-react-layout