Merge pull request #92 from camilotorresf/pin-loaders

Fixes to /admin/selection/
Add a button to change page size, fix pagination

Add a button to change the pin size.
Change a little the layout.
Fix pagination in some cases.
Edit pins: add search form
Edit pins: search pins
Edit pins: paginate and click to edit
Edit pin: show edit form
Edit pin: save changes
Edit pin: preserve rearches