[localevaluation.swipdg] fixed penalty term
[operators.elliptic-swipdg] added ctors that do not require a matrix

The operator will then create an appropriate matrix, which can be obtained
by calling matrix().
[operators.elliptic-swipdg] added first draft of make_elliptic_swipdg()
[test.operators_elliptic_swipdg] added first draft