Improve sys-mor demos

[pmli]

This PR does some major changes in sys-mor tutorials: adding more MOR methods, improving consistency across demos, and removing some code duplication and unneeded plots. Also, it reduces problem dimensions for system testing.

[codecov]

Codecov Report

Merging #1198 (3ed84b3) into master (4085263) will decrease coverage by 0.13%.
The diff coverage is 99.39%.

Impacted Files	Coverage Δ
src/pymordemos/heat.py	95.77% <97.36%> (+1.10%)	⬆️
src/pymordemos/delay.py	96.87% <100.00%> (-1.78%)	⬇️
src/pymordemos/parametric_delay.py	97.82% <100.00%> (-0.51%)	⬇️
src/pymordemos/parametric_heat.py	98.88% <100.00%> (-0.32%)	⬇️
src/pymordemos/parametric_string.py	98.79% <100.00%> (-0.91%)	⬇️
src/pymordemos/parametric_synthetic.py	98.46% <100.00%> (-0.61%)	⬇️
src/pymordemos/string_equation.py	97.10% <100.00%> (+1.25%)	⬆️
src/pymortests/demos.py	88.67% <100.00%> (+0.48%)	⬆️
src/pymor/bindings/ngsolve.py	82.08% <0.00%> (-2.53%)	⬇️
src/pymor/bindings/slycot.py	92.30% <0.00%> (-1.93%)	⬇️
... and 59 more

[sdrave]

If you use this a lot, one might consider moving (a version of) run_mor_method(_param) to pymor.algorithms.error ..

[pmli]

If you use this a lot, one might consider moving (a version of) run_mor_method(_param) to pymor.algorithms.error ..

I just used it in a few demos, but it could be worth considering having a version in algorithms.error with more features.