Resolve "Allow usage of other Kraken instances via CLI"

[btschwertfeger]

The URL passed to the CLI is now parsed correctly, allowing to communicate with other Kraken instances than the default one.

Closes #406

[codecov]

Codecov Report

❌ Patch coverage is 80.95238% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.44%. Comparing base (981aa4a) to head (68199e6).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
src/kraken/cli.py	80.95%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
+ Coverage   87.36%   87.44%   +0.08%     
==========================================
  Files          22       22              
  Lines        1963     1976      +13     
==========================================
+ Hits         1715     1728      +13     
  Misses        248      248              

Flag	Coverage Δ
unittests	87.44% <80.95%> (+0.08%)	⬆️

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

Files with missing lines	Coverage Δ
src/kraken/cli.py	87.34% <80.95%> (-0.54%)	⬇️

... and 1 file with indirect coverage changes

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