OSS updates and some extra cleanup

[shouples]

This probably should've been multiple PRs, but here we are.

Added

• Github-published documentation
• More github workflows

Changed

(mostly for ease of future development now that docs are being generated)

• Directory restructure to move under src/dx and pull tests out into their own top-level directory
• Renaming the formatters:
  • dx.formatters.dataresource -> dx.formatters.simple
  • dx.formatters.main -> dx.formatters.plain (dx.formatters.main now handles the main formatting flow)
  • dx.formatters.dx -> dx.formatters.enhanced
  • ...and all the test updates as a result of the above
• Deduplication of code to consolidate main formatting functions under dx.formatters.main where main differences in formatting are either pulled from settings based on the current display mode, or are handled deep within generate_body() to change the structure of data before being sent to the frontend

Fixed

• dx.display no longer gets mixed up with IPython.display
• datetime.date or datetime.time values should be preprocessed and cast as strings before rendering
• <dataframe>.groupby() rendering should no longer fail preprocessing