Issue 1114 r average

[valentinsulzer]

Description

• Fix r-average to allow taking r-average of a SecondaryBroadcast
• Add "R-averaged particle concentration" variables
• Fix bug in spherical integral discretisation

Fixes #1114

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 #1118 into develop will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1118   +/-   ##
========================================
  Coverage    97.82%   97.82%           
========================================
  Files          245      245           
  Lines        13273    13280    +7     
========================================
+ Hits         12984    12991    +7     
  Misses         289      289           

Impacted Files	Coverage Δ
pybamm/expression_tree/broadcasts.py	100.00% <100.00%> (ø)
pybamm/expression_tree/unary_operators.py	100.00% <100.00%> (ø)
pybamm/models/submodels/particle/base_particle.py	100.00% <100.00%> (ø)
pybamm/spatial_methods/finite_volume.py	97.86% <100.00%> (ø)

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[brosaplanella]

Looks great, thanks Tino!

[rtimms]

thanks @tinosulzer !