Remove the postgresql package in favor of simplestore

[macrael]

Description

To simplify our db situation, this PR removes the rest of the old go-pg based database code. The last stuff that it was doing related to accounts has been implemented in simplestore using the new patterns. Getting rid of the last vestiges of the db code feels good!

There are a couple things left to do:

• add Transmission support to simplestore
• re-engage the Account.validate code on account save.

Checklist for Reviewer

• Review code changes
• Review changes for Database effects
• Verify change works in IE browser

More details about this can be found in docs/review.md

[codecov]

Codecov Report

Merging #1844 into develop will decrease coverage by 4.28%.
The diff coverage is 88.76%.

@@             Coverage Diff             @@
##           develop    #1844      +/-   ##
===========================================
- Coverage    88.25%   83.97%   -4.28%     
===========================================
  Files          887      911      +24     
  Lines        20223    21501    +1278     
  Branches      3030     3219     +189     
===========================================
+ Hits         17846    18054     +208     
- Misses        1777     2478     +701     
- Partials       600      969     +369

Flag	Coverage Δ
#backend	72.28% <88.76%> (-10.87%)	⬇️
#frontend	88.98% <ø> (-1.67%)	⬇️

Impacted Files	Coverage Δ
api/http/attachment.go	89.38% <ø> (ø)	⬆️
api/http/status.go	69.23% <ø> (ø)	⬆️
api/http/save.go	83.33% <ø> (ø)	⬆️
api/http/form.go	68.97% <ø> (ø)	⬆️
api/http/refresh.go	100% <ø> (ø)	⬆️
api/simplestore/sessions.go	82.14% <ø> (-1.19%)	⬇️
api/simplestore/attachments.go	66.67% <0%> (ø)	⬆️
api/admin/reject.go	66.67% <100%> (-0.78%)	⬇️
api/admin/submit.go	70% <100%> (+2%)	⬆️
api/http/basic_auth.go	81.4% <100%> (-0.42%)	⬇️
... and 260 more

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[macrael]

@ryanhofdotgov I've got to go to bed and be done. This PR is big and good, however, the merge into the mainline is still big and to be done. I've gotten started on it but I'm not done. I would really like to get this in before we roll off, but understand if we want to code freeze instead.

I think that if you're planning to cut a full release and do a merge then it's probably worth waiting on this code, I should probably be the person to do the merge since I've been thinking about it. But I'd love for you to review it and I can address comments when I'm back.

Take Care,

[ryanhofdotgov]

This is really nice to clean up – thanks! Aside from putting that code in a transaction, my main request on this one is that we have a full round of manual testing using the downstream fork this week; i.e., merge it in a downstream branch, test it out ahead of our end of sprint. And that @kdolan-soliel understands the motivation and approach here.

[ryanhofdotgov]

It's not super important since this is code that is just used for dev, but I'd put these 2 statements in a transaction.

Doesn't affect production, can be done in follow-up