use default values in /packages and /contents (issue 15)

Currently /packages and /contents check if the query parameters are None and replace None with a default value. These default values are then passed to the template via the form variable, but these default values aren't used elsewhere in the handler. This causes issue #15 where a default value is passed to the template but not to the get_num_packages function, causing the template to think there are more packages than there actually are.

I was in a rush writing this PR and have not yet tested it. Before merging please test to make sure there aren't any bugs. I will try to test as soon as I can. I've now tested this fix and it works (although, of course, I'm not opposed to others doing additional testing).