Port pd-l2ork upstream commits from Dec 7, 2015 improving the handling of $ substitutions in GUI elements. Also fixes #195.

cleanup iemgui dialog form names, replacing dashes with underscores. Fix stray bugs in canvas dialog, and clean up css selector names

for reading preferences on Windows, try HKCU first, then fall back to HKLM. For writing, only write to HKCU

Reset the last search term after closing the canvas find dialog so that the next search restarts from the beginning again.