Reduce/sort out CKAN's dependencies

[seanh]

This ticket depends on #2423, #2424, #2425, #2426 and #2427.

• Try to remove as many of CKAN's dependencies as possible
• Try to update as many of the remaining ones as possible
• Try to get rid of some dependencies that are fetched from random hg or git servers instead of pypi
• Then try to get the order of deps in the requirements files right so that you end up with the right versions of everything
• Each module in the dependencies file should specify the exact version, to protect us from changes due to them upgrading versions under us and breaking things or changing their own deps
• Consider shipping dependencies with ckan instead of pip installing them?
• This is related to moving CKAN to Ubuntu 12.04
• Add a test case that runs pip freeze and tests that all the right versions of deps are installed?