Files Tab: Allow selection by dragging

In the [Files] tab, please allow multiple files to be selected by dragging (as if drawing a box).

This is the norm in table views, and QBitTorrent is one good example. Windows Explorer's list view is another example, although this one will include rendering of the drag box, which is not necessary for SmartGit.

The current workaround is to use Shift+Click or Ctrl+Click to select multiple files, which is a two-handed action.