Make search bar specific to reactions/metabolites/genes

[axelvonkamp]

Searching within reactions/metabolites/genes should be handled separately. If one currently searches e.g. for a reaction and then switches to metabolites the search string is still being displayed but no selection takes place (and usually should not). If one then searches within metabolites and goes back to reactions the old selection is displayed but with the metabolite search string shown. This is incosistent and can sometimes be annoying.