Issue 1030 length scales models

[valentinsulzer]

Description

Add length scales to the models, in the same way as timescale.
Also fixes a few minor things in quickplot

Fixes #1030

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 #1058 into develop will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #1058      +/-   ##
===========================================
- Coverage    97.72%   97.72%   -0.01%     
===========================================
  Files          237      237              
  Lines        12426    12413      -13     
===========================================
- Hits         12143    12130      -13     
  Misses         283      283              

Impacted Files	Coverage Δ
...models/full_battery_models/lead_acid/basic_full.py	100.00% <ø> (ø)
pybamm/models/base_model.py	98.82% <100.00%> (+<0.01%)	⬆️
...l_battery_models/lead_acid/base_lead_acid_model.py	100.00% <100.00%> (ø)
...ttery_models/lithium_ion/base_lithium_ion_model.py	100.00% <100.00%> (ø)
pybamm/parameters/parameter_values.py	99.30% <100.00%> (+<0.01%)	⬆️
pybamm/plotting/quick_plot.py	100.00% <100.00%> (ø)
pybamm/solvers/processed_variable.py	99.58% <100.00%> (ø)

---

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 00cbe19...9aa952c. Read the comment docs.

[rtimms]

great, thanks @tinosulzer !