LoaderChooser: skip abstract classes
TRSPreprocessor
TRSInlineSpeakers
cruft cleanup: removed RegExpFrame

It wasn't very user-friendly, and it's much more convenient to define regular expressions in custom preprocessors anyway.
cruft cleanup: removed ElementType
cruft cleanup: removed ElementList
UI: don't open main frame in top-left corner
UI: NicerFileChooser saves last location to disk
RawTextLoader: create speaker tracks