Fix up statusbar drawing in the wps a bit, fixing most, if not all, (re-)draw issues.

Fix up statusbar drawing in the wps a bit, fixing most, if not all, (re-)draw issues.
a) remove the temporary work around in gui_wps_display
b) let the  wps-statusbars redraw if it's masked (i.e. WPS_REFRESH_ALL or WPS_REFRESH_STATUSBAR)
c) fix a bug of mine, I attached re-fixing the bars to the wrong event
d) unify the decision whether to draw bars at all
e) some other style/code minor cleanups

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@20400 a1c6a512-1295-4272-9138-f99709370657