Improvements to package search

[rgrp]

Several things:

• Default package search (used e.g. on front page) should deal well with multiple items: "abc xyz" means search for both abc and xyz (as separate searches)
• Should automatically display a list of matching tags in a line at top with number of associated packages
• have an option to only search for fully open material (or openly licensed material ...)

Since we should be moving to a more sophisticated search solution anyway (to allow prioritisation etc) maybe we should cautious as to what we do now.