applets/timer: add compact representation

The compact representation has 5 layout forms:

1. inPanel, Horizontal: [Icon][Column to show the title and the
   remaining time]
2. inPanel, Vertical: [Column to show the title and the remaining time
   in seconds]
3. Desktop, width is enough to contain the icon and the remaining time
   in a row: [Icon][Column]
4. Desktop, width is not enough: [Icon]
                                 [Column]
5. Desktop, both width and height are not enough: [Icon]

The added compact representation also enables tab focus in the applet.

BUG: 301861
BUG: 304923
BUG: 347492
BUG: 360996
BUG: 395182
BUG: 399930
BUG: 430289
BUG: 452701
FIXED-IN: 5.26