Issue 695 export variables

[valentinsulzer]

Description

Add some more ways to export variables (matlab and csv file), to then post-process using different tools.

Fixes #695

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Merging #811 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #811   +/-   ##
=======================================
  Coverage   98.19%   98.19%           
=======================================
  Files         181      181           
  Lines       10227    10243   +16     
=======================================
+ Hits        10042    10058   +16     
  Misses        185      185           

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[Scottmar93]

All looks great!!