Rename cathode and anode

[brosaplanella]

Description

Notation has been homogenised to use positive and negative electrode (instead of cathode and anode). This applies to the options in the cracking model and lost of active material and the parameter folders.

Fixes #1333

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 #1337 (1a8b373) into develop (57ab11d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1337   +/-   ##
========================================
  Coverage    98.14%   98.15%           
========================================
  Files          272      272           
  Lines        15561    15572   +11     
========================================
+ Hits         15273    15284   +11     
  Misses         288      288           

Impacted Files	Coverage Δ
...er2019/lead_exchange_current_density_Sulzer2019.py	100.00% <ø> (ø)
...ve_electrodes/lead_Sulzer2019/lead_ocp_Bode1977.py	100.00% <ø> (ø)
...ead_dioxide_exchange_current_density_Sulzer2019.py	100.00% <ø> (ø)
...ad_dioxide_Sulzer2019/lead_dioxide_ocp_Bode1977.py	100.00% <ø> (ø)
...2019/oxygen_exchange_current_density_Sulzer2019.py	100.00% <ø> (ø)
...s/graphite_Ai2020/graphite_cracking_rate_Ai2020.py	100.00% <ø> (ø)
...aphite_Ai2020/graphite_diffusivity_Dualfoil1998.py	100.00% <ø> (ø)
...i2020/graphite_entropy_Enertech_Ai2020_function.py	100.00% <ø> (ø)
...s/graphite_Ai2020/graphite_volume_change_Ai2020.py	100.00% <ø> (ø)
...0_electrolyte_exchange_current_density_Chen2020.py	100.00% <ø> (ø)
... and 42 more

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[valentinsulzer]

We should discuss in the meeting that this is not too much of a breaking change. But the changes themselves are all good

[valentinsulzer]

Looks good, just a suggestion for an extra error check

[brosaplanella]

@tinosulzer @tlestang here are the warnings/errors you suggested, in case you want to take a look. Otherwise, let me know and I will merge the branch.