Hooked up Workspace Saving to FilePicker

Added buttons for saving and loading to the main menu and had the
WorkspaceManager launch the FilePicker and use the result to save the
the .iml
Replaced ColorRule is_fallback attribute with function

One less thing to get out of sync.
Multiple calls to FilePicker

Handled the case when the FilePicker is launched by two different menus
at once. The new launch will now trigger the onCancel function of the
old one.

Also made the save icon less ugly.