Exporter now remembers the previous file format.
Further work on UI logic for export dialog, automatically deduce file name and respond to tab changes.
ExportDialog: update caption with current file, keep export button disabled while no scene is selected.
Assimp-net: add Node.MetaData attribute when WITH_NODE_METADATA is set. This is needed for native marshalling with the export API when using the assimp trunk.
Export dialog: Progress display and failure handling
Export UI tweaks, implement "open exported file" checkbox.
Merge pull request #5 from acgessler/export

Export v1