OK - so I have to admit I *hate* the fact that PIP seems to require a
subdirectory named like the library.
But since the PIP package is something really nifty to have (thanks to
@tony again!!!), I updated the codebase to hopefully conform with what
PIP expects. Testruns so far look promising...
Add two new parameters: theme and iconset
Add a placeholder class core.theme.Theme, an instance of which is passed
in to the i3 output object (which is the only object that should ever
have need of the theme, hopefully).
