This reverts commit 716233534b.

It causes issues with truncation of characters when the text does not fit and
so on.  The patch should be reworked and properly tested.

Calculates len & ew in drw_font_getexts loop by incrementing instead of
decrementing; as such avoids proportional increase in time spent in loop
based on provided strings size.

The function drw_fontset_free in drw.c was never called.

- better scaling for occupied tag squares.
- draw statusline first to omitt some complicated calculations.

important:
- drw_rect: didn't use w and h, change the dwm code accordingly.
- drw_text: text is NULL is not allowed, use drw_rect().

however renamed theme into scheme resp. Theme into ClrScheme