Add BatchStudy examples

[Saransh-cpp]

Description

Added an example notebook describing pybamm.BatchStudy. The notebook compares models, parameter values, and summary variables. Please let me know if there are some other interesting comparisons that I should add in here.

Fixes #1492
Fixes #1745

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 #1747 (da05ff8) into develop (9b5d303) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1747   +/-   ##
========================================
  Coverage    99.28%   99.28%           
========================================
  Files          343      343           
  Lines        18864    18868    +4     
========================================
+ Hits         18729    18733    +4     
  Misses         135      135           

Impacted Files	Coverage Δ
pybamm/plotting/quick_plot.py	99.71% <100.00%> (+<0.01%)	⬆️

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[valentinsulzer]

Awesome, thanks! I think you can also do the quick fix for #1745 ?

[Saransh-cpp]

Awesome, thanks! I think you can also do the quick fix for #1745 ?

Yes, should I add a "breaking change" for renaming solutions to input_solutions?

[valentinsulzer]

Yes, should I add a "breaking change" for renaming solutions to input_solutions?
solutions doesn't need to be renamed to input_solutions, as far as the user is concerned nothing is changing. If you do

input_solutions = solutions
solutions = []

then input_solutions will still be the original solutions and solutions will become []

[valentinsulzer]

thanks for fixing my mess haha