Issue 991 simulation inputs

[valentinsulzer]

Description

Fix a bug to allow parameter fitting using the simulation with experiment

Fixes #991

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 #1000 into develop will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1000   +/-   ##
========================================
  Coverage    97.56%   97.56%           
========================================
  Files          233      233           
  Lines        12106    12109    +3     
========================================
+ Hits         11811    11814    +3     
  Misses         295      295           

Impacted Files	Coverage Δ
pybamm/parameters/parameter_values.py	100.00% <100.00%> (ø)
pybamm/simulation.py	98.41% <100.00%> (+<0.01%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8f0a6d8...a43ba6c. Read the comment docs.

[brosaplanella]

Look good to me, thanks Tino!