Implement e-prop plasticity #4923

Job	Run time
black	26s
clang-format	20s
copyright_headers	22s
cppcheck	4m 17s
flake8	22s
forbidden_types	14s
isort	11s
lychee_IGNORED	35s
mypy	36s
pydocstyle	21s
pylint	36s
rstcheck	22s
unused_names	15s
vale	28s
sphinx-rtd	3m 10s
sphinx-conda	0s
build_macos (macos-latest, clang, openmp, mpi, python, gsl, ltdl, boost, hdf5, optimize, warning)	23m 40s
build_linux (ubuntu-20.04, gcc, boost, optimize, warning)	12m 2s
build_linux (ubuntu-20.04, gcc, openmp, python, gsl, ltdl, boost, optimize, warning)	18m 18s
build_linux (ubuntu-20.04, gcc, mpi, python, gsl, ltdl, boost, optimize, warning)	19m 0s
build_linux (ubuntu-20.04, gcc, openmp, mpi, python, gsl, ltdl, boost, hdf5, sionlib, libneurosim...	25m 2s
	1h 50m 37s

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