Price forms fixes: part of CRM-19517 + cleanup & symptom fix for CRM-19953

[eileenmcnaughton]

I pulled in a portion of @seamuslee001 PR for CRM-19517 - ie the part with the component check & making it editable. I made some changes to it

• added a distinct into the component query
• used the api rather than changing the BAO function. Ideally we would add a unit test to the api to enforce respect for 'check_permissions'
• altered the edit form to load - I was still hitting a permission error there.

I didn't pull in all parts because I felt these changes stood alone and could go in without the rest. I had reservations about some of the other part I looked at because I saw the contribution forms were using a shared process to add price fields to the form & the event fields were using different methods & I felt they really needed to be consolidated.

This PR contains fix in a related area of code - basically tidy up around the getUsedFor function to

• extract the chunks of code within the function & add comments
• Remove call to the (sometimes slow) getUserFor from DeleteSet as delete set is only called in one place, which is right after the same call has been checked
• only call getUsedFor from the api if 'return' has not been set. This fixes the immediate issue - ie. the contribution view page which calls that api with 'return' and can hit slowness

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• CRM-19517: Show price field Options that use disabled Financial Types so they can be edited.
• CRM-19953: Performance issues on price set retrieval

[seamuslee001]

I am going to approve this noting that there is still work to solve the display of the price sets. Eileen has indicated she wants to unify this. I have verified that fields / options with no active financial type do not show on public pages but are visible on the edit pages

[eileenmcnaughton]

Merging per @seamuslee001 review (thank you)