The native FolderBrowserDialog has the usability of a brick. We already use WindowsAPICodePack's dialog in the launcher form, so we might as well use it in the preview form too. It'll make testing stuff that needs this dialog a lot easier too.
Renamed ShowEntityFolderSelect to OutputFolderSelect, and made it used by both entity and bitmap exporters. This function now returns a bool on success.
Both calls to OutputFolderSelect now do so inside of BeginInvoke, because otherwise the menu items will draw over top of the dialog while its showing... GG windows...