#958 added export_csv to parameter values and relevant tests

[Scottmar93]

Description

Added a helper function to parameter values to export the whole dictionary as a csv file.

Fixes #958

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 #959 into develop will increase coverage by 0.00%.
The diff coverage is 97.77%.

@@           Coverage Diff            @@
##           develop     #959   +/-   ##
========================================
  Coverage    97.56%   97.56%           
========================================
  Files          233      232    -1     
  Lines        12109    12119   +10     
========================================
+ Hits         11814    11824   +10     
  Misses         295      295           

Impacted Files	Coverage Δ
pybamm/parameters/parameter_values.py	99.63% <97.77%> (-0.37%)	⬇️

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[valentinsulzer]

thanks @Scottmar93

[valentinsulzer]

Having now read the issue, can you also move print_parameters to be a method of the ParameterValues class?