Search fixes & improvements

[Oaphi]

closes #1128

This PR ensures votes: operator can use negative values:

Does a general cleanup of qualifier parsing as well in preparation for #1760

[codecov]

Codecov Report

❌ Patch coverage is 88.04348% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.78%. Comparing base (4153f8d) to head (9f32949).
⚠️ Report is 13 commits behind head on develop.

Files with missing lines	Patch %	Lines
app/helpers/search_helper.rb	37.50%	10 Missing ⚠️
app/helpers/search_qualifier_helper.rb	98.68%	1 Missing ⚠️

Additional details and impacted files

Components	Coverage Δ
controllers	69.86% <ø> (ø)
helpers	81.82% <88.04%> (+2.62%)	⬆️
jobs	60.00% <ø> (ø)
models	86.12% <ø> (ø)

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[Oaphi]

Not particularly concerned with covering 100% of the change as we didn't have a single test case before it in the first place - I've added as many as I could for now, we can easily expand on them later. More concerned about manually confirming search works as expected after the change (seems so, but another pair of eyes on it would be nice)

[cellio]

Tested: votes:-1 returns net votes exactly -1, likewise -2 and 0. votes:<=-1 correctly pulls in -2. Behavior looks good to me.

[cellio]

I tested the behavior and reviewed the test cases. I didn't review the implementation code.