Refactor get_matrices_from_linear_ode function

[smover]

The function implementation duplicates code that we already have. You can replace the implementation of get_matrices_from_linear_odes only with the two lines above.

My proposal is to 1) move the function get_matrices_from_linear_ode as a method of the DynSystem class in barrier/systems.py (so, you would use it as system.get_matrices...() ) and 2) replace the implementation with the two lines above.
So, you will have this function ready just by looking at the interface of a DynSystem.

For now it's ok to keep it as is, we will refactor later.