Add self cal algorithm and example script

[matmanc]

No description provided.

[codecov-commenter]

Codecov Report

Merging #3 into master will increase coverage by 0.27%.
The diff coverage is 84.88%.

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
+ Coverage   80.30%   80.57%   +0.27%     
==========================================
  Files           6        6              
  Lines         523      587      +64     
==========================================
+ Hits          420      473      +53     
- Misses        103      114      +11     

Impacted Files	Coverage Δ
lofarimaging/singlestationutil.py	83.06% <64.28%> (-2.14%)	⬇️
lofarimaging/lofarimaging.py	86.02% <94.82%> (+5.78%)	⬆️

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