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).
Add logic for parsing commandline options, and a preliminary stub for
loading modules.
Note: The idea is that core.module.load() will return a valid, but
empty, module that displays an error, if the module cannot be loaded
