Cleanup the way FX Dialogs are handled

[jpasqua]

All the dialogs based on FXML use kind of a hack to supply parameters. They are passed in a circuitous manner through a hash table. This is awkward and error prone. Also, clients of the Dialogs must specify the cxml resource files for the dialogs. They should know about those resources. Clean up the way dialogs work to get rid of both of these problems.