SW-98. SW-79. Convert openviz. package imports and general file updates

Same details as previous commit. This commit includes the BspEmulator and
SimEngine sub-packages.
Also adapted docs to the top-level openvisualizer package.
SW-98. Move openUI package to openvisualizer sub-package. Finish docs.

Sphinx documentation now builds cleanly.
SW-98. Fix bug in call to os.path.join()