fix: base cog api now works

[abluey]

Summary

Closes #388

Incorporated Jack's code for making JSON posts work Removed package parameter requirement for loading and unloading cogs (this was requested a while ago).

Checklist

• [x] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
• [x] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

• [x] Have you tested the changes? (pytest & dpytest)
• [ ] Have you followed PEP-8 for naming and styling?
• [ ] Has your code been properly documented with RestructuredText docstrings?
• [ ] Have you added your changes to CHANGELOG.md under the [Unreleased] heading?
• [ ] If your code added new bot commands, have you updated documentation.json?

• [x] All of this code is your own, or follows the author repo's licence.

[codecov[bot]]

Codecov Report

Merging #398 (21aa650) into master (b7822ad) will decrease coverage by 0.03%. The diff coverage is 97.95%.

@@            Coverage Diff             @@
##           master     #398      +/-   ##
==========================================
- Coverage   86.77%   86.75%   -0.03%     
==========================================
  Files         111      111              
  Lines        8166     8161       -5     
==========================================
- Hits         7086     7080       -6     
- Misses       1080     1081       +1     

Flag	Coverage Δ
unittests	86.75% <97.95%> (-0.03%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
koala/rest/api.py	85.45% <75.00%> (-1.09%)	:arrow_down:
koala/cogs/base/api.py	98.43% <100.00%> (ø)
koala/cogs/base/cog.py	97.11% <100.00%> (ø)
koala/cogs/base/core.py	96.51% <100.00%> (ø)
tests/cogs/base/test_api.py	100.00% <100.00%> (ø)
tests/cogs/base/test_core.py	98.65% <100.00%> (ø)

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