issue #1 add categories

change the search page layout to group results by categories.
change database search to return category too.

@todo: add delete in search results.
issue #1 no more SQLite legacy code

not everything is tested though, not daring to delete an user yet
Some optimizations according to issue #2
introduce common SQL function with error handling
Merge branch 'issue#1'

Conflicts:
	PDO.php
	search.php
issue #1 merge destroyed db_getCatName()