ENH: Implement add folder button, options window (select and override colors.list default)

[ngAlexander9]

Added a new button to add folders to the list of files to convert.
It takes the folder and traverses through, selecting only files which can be converted. When generating the output file, it preserves the directory structure. For example, if the examples folder is added (examples/*.edl), the output files will be [output folder]/examples/*.ui.

Added the ability to set a flag to override the default colors.list, and provide the alternate path. #6

The options window provides rudimentary checking (does the file exist), but doesn't evaluate if the provided file is a valid colors.list content. Providing this file to the converter/parser is not yet implemented (will be in the convert method in main window)

Also added the select output folder in the General tab. Same behavior as the modal.

There could be improved styling in the options window....

Generalized the file-selection widget into its own component. It is a line edit and a button that opens a file dialog. Pretty handy interface element used in several locations.

Switched some print statements to use logging. These get formatted by pydm's logging configuration.

Also a tiny bugfix. Shouldn't set the mainwindow as the parent of optionswindow, otherwise the elements render in the same window. oof.

If you try to launch, it suffers from the circular import error (dataclasses.py interferes with dataclasses). Renaming the file resolves that issue. I figure I'd leave it to the others to change the filename.