[Tiles view] keyboard interaction

[kulmann]

The keyboard interaction possibilities that we provide for the list view don't work in the tiles view. The current implementation should be adapted so that it can be used in a generic, parameterized way as follows.

• navigating through the list:
  • list view: arrow keys up/down
  • tiles view: arrow keys in all four directions
• toggle selection: space bar (for all view types)
• extend selection (having one or more items already selected and adding more via keyboard or keyboard+mouse):
  • list view: shift + click extends the selected rows up/down to the clicked one
  • tiles view: shift + click extends the selected tile up/down to the clicked one in a rectangle 😄 🤓
  • for both list & tiles view: ctrl + click adds the clicked row/tile to the selection
• clear selection: ESC (for all view types)