Access SAPI 5 via the pythoncom/win32com modules

Removes the Python code that interacted with cscript and the JSript glue
script and instead attempts to do this all in Python with the pythoncom
and win32com modules instead.
Drop disused SAPI 5 JScript gateway code

Also adjusts the migration code and two helper scripts.
Workaround for gen_py path issue on some installs

Some Anki installations will not have a working __gen_path__ when
starting up, so we can fix this by repointing it at the user's temporary
directory.