"Other" changes from the julia branch

[valentinsulzer]

Description

The Julia branch is not ready yet, but there are some other changes that might be useful for the print-equations project that I would like to merge in (mainly, defining "print_name" for other variables)

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 #1497 (2e4f5e4) into develop (28de127) will increase coverage by 0.00%.
The diff coverage is 99.19%.

@@           Coverage Diff            @@
##           develop    #1497   +/-   ##
========================================
  Coverage    98.34%   98.34%           
========================================
  Files          296      296           
  Lines        17104    17141   +37     
========================================
+ Hits         16821    16858   +37     
  Misses         283      283           

Impacted Files	Coverage Δ
pybamm/solvers/casadi_solver.py	100.00% <ø> (ø)
pybamm/util.py	100.00% <ø> (ø)
...bamm/expression_tree/operations/evaluate_python.py	97.78% <80.00%> (ø)
pybamm/__init__.py	94.95% <100.00%> (ø)
pybamm/expression_tree/concatenations.py	98.13% <100.00%> (+0.07%)	⬆️
pybamm/expression_tree/functions.py	100.00% <100.00%> (ø)
pybamm/expression_tree/parameter.py	100.00% <100.00%> (ø)
pybamm/expression_tree/scalar.py	100.00% <100.00%> (ø)
pybamm/expression_tree/variable.py	100.00% <100.00%> (ø)
pybamm/models/base_model.py	99.23% <100.00%> (+<0.01%)	⬆️
... and 5 more

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[rtimms]

thanks @tinosulzer , looks good!

[rtimms]

can this and the concatenation for T be removed?