Initial support for thumbnails and grid view.

Added thumbnail_location key to Asset and has_thumbnails key
to AssetCollections; modified routes to handle new show_grid
action for AssetCollectionController as well as new view
based on RatioGrid.
Grid view now takes advantage of median_thumb_length attribute
Make grid view respect order on display.
Added page-by-page display of assets within a collection.

This new method duplicates the javascript-centered page navigation
screen, but does all image loading on the server side.  It is more
appropriate for large asset collections whose image files cannot
easily be loaded into browser memory all at once.  Pagination will
be slower than the old AssetCollectionController:show action, but
will be possible.
Fixed off-by-one error with Asset.order for page numbers
add filter feature to asset_collections
wrap form_for inside a div
tweak form
rename test to filter
tweak css a bit
add some data to views
add start_date and end_date in views
Convert raw HTML elements to rails helper methods
Oops
Fix view
format code
Initial search integration
Add proper date elements
revert
Add date inputs