Do not show unsearchable columns in quicksearch

The quicksearch on the navigation bar is still in use in Chemistry. Now we are moving to storing pictures as bytea columns rather than oids we see the bytea column appear as a column to be searched in the quicksearch which makes no sense as these can't be usefully searched with that interface. This updates the quicksearch to exclude columns of type bytea and oid and tidies up some long-commented lines.

Closes #3 (closed)