visualisation for tagclips

To keep things cheap, only tagged areas inside the editing grid are shown.
I added two variables, tagnum and taglife, to allow playing with the
parameters of the sparklies. Those should be removed later. The default
values work quite well on my really crappy onboard graphics card. Higher
values start dropping fps.

Also, the edit status line now shows the tag value of the cube pointed at.

The patch also fixes the bug, that the edit status line did not show
details about the selection, unless there was at least one entity in the
map.