Revert plugin breakage 12476 (rebased onto develop)


This is the same as gh-2842 but rebased onto develop.

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Fixes https://trac.openmicroscopy.org.uk/ome/ticket/12476 by reverting most of https://github.com/openmicroscopy/openmicroscopy/commit/81ac72e50e16741b83343c823e522eda7639d452 

This shouldn't have any effect on behaviour. Check that webclient search still works OK and displays results as before.
Discussed with @dpwrussell and he's probably not going to revert his fix (keeping his duplicate to protect us from future breakages).

Also addressed comments on https://github.com/will-moore/openmicroscopy/commit/3488ca43dda3f19c836edfd2dc222d19442b015f from @aleksandra-tarkowska.
To test:
 - check that the search page group-user dropdown doesn't have a thick black border
 - check the other main pages (webclient home page, history page, tags etc)
 - check that webtagging_search page looks OK.