Fix SevenTV emote resolver

[pajlada]

Pull request checklist:

• CHANGELOG.md was updated, if applicable

Description

The API url used for the SevenTV resolver was broken - this PR fixes this and adds a lot of tests to prevent this from happening again.

[codecov]

Codecov Report

Merging #281 (9428edd) into master (e5e4d1a) will increase coverage by 2.56%.
The diff coverage is 70.58%.

@@            Coverage Diff             @@
##           master     #281      +/-   ##
==========================================
+ Coverage   29.54%   32.10%   +2.56%     
==========================================
  Files          56       56              
  Lines        1723     1713      -10     
==========================================
+ Hits          509      550      +41     
+ Misses       1178     1130      -48     
+ Partials       36       33       -3     

Impacted Files	Coverage Δ
internal/resolvers/seventv/emote_loader.go	80.21% <54.54%> (+21.80%)	⬆️
internal/resolvers/seventv/emote_resolver.go	100.00% <100.00%> (+100.00%)	⬆️
internal/resolvers/seventv/initialize.go	100.00% <100.00%> (+100.00%)	⬆️

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