Initial checkin of Gtk rewrite

- Rewrite xdsc in Python/Gtk3
- Provide the Glade UI file for the new xdsc
- Provide an icon for xdsc (stolen from diswww)
Remove C version
Update man page
Tweak font and UI

- Per andersk's suggestion, Use Gio.Settings to determine the preferred
  monospace font, rather than hardcoding Courier.  However, we don't use
  get_string() since that segfaults if the string isn't there.  Fortunately,
  Gio.Settings pretends to be a dictionary.
- Add a margin in the transaction textview widget
Change default path for UI and icon file

The package is not debathena-specific, so we should use our own
directory in /usr/share
Clean up comments in get_meeting()

Explain why we do the check_update() hack, and remove incorrect
comments in docstring about caching connections.
Don't call invalid methods

Fix some leftover code from the DiscussWrapper rewrite.
Use new RCFile.delete() method

Use RCFile.delete() instead of writing our own.
Rename xdsc.py to xdsc

Remove the .py suffix, because our various 2014 install systems
still don't support renaming files when installing them, despite
the fact that install(1) has supported this since forever.
Add a distutils setup script

Add a setup.py script, since we're going to pretend this software
is useful outside of Project Athena
Merge branch 'master' into debian
Update Debian packaging for xdsc 10.1

- This is a complete rewrite in Python, so update the control file,
  rules, and changelog as appropriate.
- Update the copyright file to the new copyright format
Add a .manpages file

Because distutils is incapable of dealing with manpages, we let
debhelper do it for us.