Refactor construction of Eclipse input tables

[berland]

The code in equil.py for printing an Eclipse input table has been generalized so it can be used for
other keywords.

[codecov-commenter]

Codecov Report

Merging #381 (b23b224) into master (81a24ac) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head b23b224 differs from pull request most recent head f7158c5. Consider uploading reports for the commit f7158c5 to get more accurate results

@@            Coverage Diff             @@
##           master     #381      +/-   ##
==========================================
+ Coverage   98.16%   98.18%   +0.02%     
==========================================
  Files          24       24              
  Lines        3318     3357      +39     
==========================================
+ Hits         3257     3296      +39     
  Misses         61       61              

Impacted Files	Coverage Δ
ecl2df/common.py	99.71% <100.00%> (+0.05%)	⬆️
ecl2df/equil.py	100.00% <100.00%> (ø)

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[berland]

Comments:

• Statements valid for py36/pandas 1.1.5 can be removed as of now
• Only the equil module is directly affected by this PR, and should be tested sufficiently already.
• This PR adds additional tests on the table generator using COMPDAT as an example, which is relevant for future feature enhancements to the COMPDAT module (and others).