This is using opacity of 0% to hide them - this way the space stays allocated
and showing it doesn't rearrange things. Using visiblity here causes
everything to shift around on reveal.
The default size of the drawings is a bit small now, good for an overview but
not for identifying which drawing to use now. Add a zoom slider for that.
This broke at some point, let's fix it again by moving to the drawing and
calling refresh() from there - no need for the DrawingPerspective to call into
the drawing here.
Drop the user-visible separation, make everything just Tuhi. Directory
structure remains largely separate (tuhi vs tuhigui) except for the po files
which are in the top-level directory because convention.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>