Vectorization opportunity generator's complexity not fit for jacobians

Although, only important to a lesser degree, the generation of jacobian_* methods can become prohibitively slow due to the sheer number of vectorization opportunities to check. Example: The verify_app_poisson_dg_tensor target has 180990 possible strategies in jacobian_skeleton, where alpha_skeleton only has 308...

Note: Due to this issue the sumfact/poisson_dg_tensor test is disabled right now.