ensure working examples

• ensure adaptive_elliptic_swipdg.cc works
• ensure adaptive_interpolation.cc works
• ensure elliptic_lrbms_fom.cc works
• ensure mpi_2019_02_talk_on_hyperbolic_equations.cc works
• ensure stationary-heat-equation.cc works
• ensure gamm_2019_talk_on_conservative*.py works
• ensure examples are compiled and executed in the CI