allow removing multiple constraints at once

[Irieo]

Make possible to pass a list into remove_constraints() to remove multiple constraints at once.
Keeps old functionality, i.e. it is still possible to pass constraint name as a string.
Adds logging, so user can see what constraints are removed.

to remove all constraints:
n.model.remove_constraints(list(n.model.constraints))

to remove a single constraint:
n.model.remove_constraints(['Bus-nodal_balance'])
or
n.model.remove_constraints('Bus-nodal_balance')

closes #210

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (930ceae) 89.26% compared to head (148a545) 89.28%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
+ Coverage   89.26%   89.28%   +0.01%     
==========================================
  Files          15       15              
  Lines        3354     3359       +5     
  Branches      771      773       +2     
==========================================
+ Hits         2994     2999       +5     
  Misses        248      248              
  Partials      112      112              

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[FabianHofmann]

Are you fine, if I set the logging from info to debug?

[Irieo]

Are you fine, if I set the logging from info to debug?

sure!