Dashboard Searching/Filtering

[davea]

This PR:

• Wires up the ordering dropdown and filters on the right-hand side of study lists (e.g. homepage, search page, user study dashboard)
• Allows the search field in the header to be used for searching by PI name, study title, country or topic
• Also generates proper links to search page in study detail header and search result entries

For #1

[stevenday]

Hound pendantics aside, this looks great. I only have a couple of general comments:

• archived studies should be a separate checkbox rather than one of the study stage options. There's a toggle link and controller action set up for this already (it sets @study_scope before you do any other filtering or sorting), it just needs bringing into the main form I think.
• The search needs to include reference numbers as well (it's great that you got all the other things into it though, thanks!)
• I think we need a bigger message in the main list_of_things template (or in the views that include it perhaps) to say when a search doesn't match any results.