Append Operator to LinearAdvectionLaxFriedrichs, Concatenation and ComponentProjection

[pmli]

Closes #989.

[codecov]

Codecov Report

Merging #1046 into master will decrease coverage by 0.01%.
The diff coverage is 73.58%.

Impacted Files	Coverage Δ
src/pymor/reductors/basic.py	77.77% <33.33%> (ø)
src/pymor/operators/ei.py	66.40% <50.00%> (ø)
src/pymor/operators/constructions.py	84.70% <52.94%> (-0.13%)	⬇️
src/pymor/discretizers/builtin/fv.py	66.92% <70.00%> (+0.06%)	⬆️
src/pymor/algorithms/image.py	80.00% <100.00%> (ø)
src/pymor/algorithms/preassemble.py	81.25% <100.00%> (ø)
src/pymor/algorithms/projection.py	78.85% <100.00%> (ø)
src/pymor/algorithms/to_matrix.py	99.17% <100.00%> (ø)
src/pymor/discretizers/builtin/list.py	84.84% <100.00%> (ø)
src/pymor/operators/interface.py	86.20% <100.00%> (ø)
... and 2 more

[sdrave]

LGTM.

Maybe it would be nice to have functions Concatenation etc. which are marked with @deprecated for the next release.

[pmli]

Maybe it would be nice to have functions Concatenation etc. which are marked with @deprecated for the next release.

Agreed. Does it look ok?

[renefritze]

Should we maybe start to a running list of deprecations in the release notes? Would make writing them a bit simlper.

[pmli]

Should we maybe start to a running list of deprecations in the release notes? Would make writing them a bit simlper.

Sounds good to me. I've added a remark to the release notes.