Replace Export Image, Alignment and Save as .. submenus with dialogs

The growing export options for file types and images make the Export submenu a bit unwieldly. Instead, we should provide a dialog box that allows:
* choice of destination: file, clipboard.
* choice of export format
 - EPS, PNG, SVG, HTML
 - Alignment formats
* additional options appropriate to each format
 - lineart/etc
 - include/exclude original data for formats that support it
 - Include exclude annotation/hidden regions for alignment format export