make quickplot use scaling from solutions

[TomTranter]

Description

Quickplot now uses timescale and lengthscale evals from the solution instead of evaluating them.

Fixes # 1233

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 #1234 (1483504) into develop (d3b1cca) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1234      +/-   ##
===========================================
- Coverage    97.95%   97.95%   -0.01%     
===========================================
  Files          250      250              
  Lines        14399    14397       -2     
===========================================
- Hits         14105    14103       -2     
  Misses         294      294              

Impacted Files	Coverage Δ
pybamm/plotting/quick_plot.py	100.00% <ø> (ø)

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[brosaplanella]

Looks good, just the minor point on the CHANGELOG. Thanks Tom!

[TomTranter]

@tinosulzer @rtimms some of the lines I changed don't actually seem to be used for anything. self.length_scales is defined but as far as I can tell never used anywhere. I commented them out and ran tests locally and they all passed. I also ran a 1+1 script and plotting the heat maps works ok without these lines. It does fail when the height is an input though. Not sure if worth fixing as I can't think of a scenario when you'd want to have height as input when doing 1+1. Similarly I guess 2+1 will not like when height and width are inputs. I could add some more informative error messages

[rtimms]

yeah it looks like the length scale stuff gets handled in processed variable. and I agree it doesn't make sense for height to be an input in 1+1D as you're changing the geometry. maybe in battery_geometry we should raise an error if any of the parameters are inputs since you can't change the geometry on the fly