Support event-assignments to compartments

[dweindl]

Not supported yet:

AMICI/python/sdist/amici/sbml_import.py

Lines 1630 to 1635 in 8c3b59a

	raise SBMLException(
	"Could not process event assignment for "
	f"{str(variable_sym)}. AMICI currently only allows "
	"event assignments to species; parameters; or, "
	"compartments with rate rules, at the moment."
	)

Test case: https://github.com/sbmlteam/sbml-test-suite/blob/release/cases/semantic/00945/