Issue 943 initial conditions

[valentinsulzer]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes #943

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

@@           Coverage Diff            @@
##           develop     #951   +/-   ##
========================================
  Coverage    98.06%   98.06%           
========================================
  Files          220      220           
  Lines        11360    11370   +10     
========================================
+ Hits         11140    11150   +10     
  Misses         220      220           

Impacted Files	Coverage Δ
pybamm/simulation.py	97.04% <100.00%> (+0.01%)	⬆️
pybamm/solvers/base_solver.py	99.48% <100.00%> (+0.01%)	⬆️

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[rtimms]

looks good thanks!