Generalise the subrecord form collapse behaviour

Make instances collapsible.

Fix subrecordcreated.aspace event being triggered twice for a newly created subrecord.
Clean up add-as-you-go link styling
Fix table cell column transparent if it overflows - make it white so it can be easily read.

Fix misaligned table header text and sort arrow.
Fix dropdown menu links text alignment
Fix accession toolbar markup (extra </div>) when suppressed
Merge pull request #684 from hudmol/collapsible-instances

[Delivers #64612226] Collapsible instances