[REF] Consolidate retrieval of searchFormValues

[REF] Consolidate retrieval of searchFormValues

Currently there are 3 ways in which the values from the searchForm are retrieved

1) the search form sets a value 'searchFormName' on the form during search which can
be later retrieved
2) the search task has an action that reflects the form it came from
3) as per 2 but there is additional handling for the fact it might be
the contact search (knowable because the entity has been set to 'Contact'

I'm not 100% sure at this stage that the selected method (3) in this PR is the best -
but it seems 'as good' as 1 with less form-state stuff and this PR consolidates it
into 1 place so it is handled consistently