CSS PM notifications: apply patch for prosilver and subsilver2 templates

This gets rid of the javascript popup notification that's blocked by
pretty much every modern browser that cares about its users, and
replaces it with a position:fixed CSS-styled box.

The original proof-of-concept patch for prosilver was provided by
Gambit and went through many modifications ever since. The final
version for prosilver spent at least one year and a half baking.

Only modifications for prosilver and subsilver2 are provided here.
No style or imageset changes are needed since all new CSS is inline.
AcidTech already has a big notification block in overall_header,
so it's excluded from this commit.