Reorder across pages

This fixes #2254. Im not sure if 2-0-stable is the correct branch, but i can add it to master if you want. This is not yet completed, it needs some specs, but i would like to discuss the functionality before giving it the last touch.

Here is a demo of the reordering across pages (the animation speed is higher in 'real life'):
![Reorder Across Pages Demo](http://f.cl.ly/items/1i0f3p2P3k3s3w3d0x0b/output_optimized.gif)

In short, does this PR implement/change the following:
* When updating positions, use the nestedSortable jQuery plugins serialization method instead of jQuery Serialize List plugin (that now can be removed)
* Simplify and fix the update position controller actions in crud
* Change how list_reorder and sortable lists works, so we can continue reordering when changing pages with ajax pagination
* Adding the ability to drop `li` elements on pagination links when reordering (se demo)