Make dashboard elements drag-drop-able

[Fohlen]

Currently the dashboard elements are in a fixed position. It would be good if every element could be dragged and dropped at the users will. To do this, I propose the following system:

• every row can have up to two elements (one on the right, one on the left)
• if there is a free place in one row you can drag another element to that place
• if you drag an element to a place that has already been filled, it will switch places with the existing element

This can be done using the drag drop API

• Make elements drag / drop-able
• Store element positions in selection module and it to the paths (so it will be restored on reload)