Add support for multiple categories and sub-categories

[Jono Bacon]

A goal for 0.2 is to add suport for multiple categories as well as sub-categories. They will be added in a format such as this to the .accomplishment file:

    depends = Development, Launchpad:Your Profile

Here multiple categories are divded by a comma and a sub-category is defined using a colon (Category:Sub-category).

[Jono Bacon (jonobacon)]

Attached to this bug report is support for sub-categories in the viewer. Some notes:

 * The sub-category view is only shown when a category is selected. Otherwise the sub-category arrow sliders are not shown.
 * Every category has an 'Other' sub-category added which should show all accomplishments in that category that don't have sub-categories assigned.
 * The arrows should be be insensitive when the number of sub-categories don't require the arrows to scroll. I haven't figured out how to do this yet, so they are always sensitive right now.

From an implementation perspective this is how it works:

 * update_views() calls subcats_show() which generates the subcats section.
 * Inside subcats_show() we call get_subcats() which should talk to the daemon and return a list of sub-categories for the currently selected collection and category. Currently get_subcats() is in the viewer and returns hard-coded data to demonstrate the feature, but get_subcats() should probably be in the daemon.
 * This branch does not include support for multiple categories, but just subcatories.

[Jono Bacon (jonobacon)]

Oh, and be sure to update lp:ubuntu-community-accomplishments/0.2 as this includes some accomplishments with this new format for categories.