Select and drag multiple elements

[klues]

In the edit view of a grid it should be possible to:

• select and drag
• delete
• edit actions

for multiple elements at once.

[klues]

First draft using jquery dragable and jquery selectable in this branch:
https://github.com/asterics/AsTeRICS-Ergo-Grid/tree/bklaus/select-and-drag-multiple-elements

[ms-mialingvo]

This would be an important feature. It should include the option to

• set the cell background color
• set the cell border (Choice to color the whole button or just make a colored edge on the button #259)
• set the level (Progressive Language Feature #344)
  in multiple cells at once

[klues]

Another related issue reported by @arasaac-dga: moving a single element around shouldn't result in changed positions of all cells "touched" while moving, but only at the final destination.

Also related: new elements should either be added at the place where the right-click was made or (if selected via "more" menu) on the next free spot in with respect to rows (not columns as now).