added option to tikz.py Plot to plot data from files

[PetrDvoracek]

I would like to contribute with new functionality, to be able to plot data from file.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.16%. Comparing base (62d9d99) to head (d446198).
⚠️ Report is 63 commits behind head on master.

Files with missing lines	Patch %	Lines
pylatex/tikz.py	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #262      +/-   ##
==========================================
- Coverage   90.44%   86.16%   -4.28%     
==========================================
  Files          60       44      -16     
  Lines        4261     2697    -1564     
==========================================
- Hits         3854     2324    -1530     
+ Misses        407      373      -34     

Files with missing lines	Coverage Δ
pylatex/tikz.py	74.82% <33.33%> (-17.24%)	⬇️

... and 58 files with indirect coverage changes

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