[#9] Reorder updated datasets on home page.

Uses modified_date if supplied, and CKAN's
metadata_modified field if not.
[#9] Change recently updated 'view all datasets' link to sort by modified_date
[#9] Make sure all ecportal plugins are loaded in test-core.ini
[#9] Small test cleanup (PEP8 and refactor search data)
[#9] Add test for sorting by modified_date