add BatchStudy class

[actualpriyanshu]

Description

Add class to compare different models and conditions

Fixes #906

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

[actualpriyanshu]

What does solver_stats and export_data do?

Could you please check it? You can run this code here
https://colab.research.google.com/drive/109KJSumPxzxi3OToN6N8g6wjuD5Yb2oe?usp=sharing

[valentinsulzer]

Thanks @priyanshuone6 , on the right track. See comments, and needs a unit test

[actualpriyanshu]

Thanks @tinosulzer
I am working on the unit tests, will add them soon. I have also fixed few other things I found and pushed them in the same PR rather than making a new one, hope you don't mind 😃

[codecov]

Codecov Report

Merging #1455 (6529de7) into develop (4205951) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 6529de7 differs from pull request most recent head 7edf780. Consider uploading reports for the commit 7edf780 to get more accurate results

@@           Coverage Diff            @@
##           develop    #1455   +/-   ##
========================================
  Coverage    98.34%   98.34%           
========================================
  Files          281      282    +1     
  Lines        16516    16563   +47     
========================================
+ Hits         16242    16289   +47     
  Misses         274      274           

Impacted Files	Coverage Δ
...m/models/full_battery_models/base_battery_model.py	99.67% <ø> (ø)
pybamm/__init__.py	94.95% <100.00%> (+0.04%)	⬆️
pybamm/batch_study.py	100.00% <100.00%> (ø)

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[valentinsulzer]

Thanks @priyanshuone6 , can you just add the other options for the Simulation? parameter_values, var_pts, etc
Also add the options for solve