Clean examples

[hverhelst]

After #12, with #10 and #11

We provide the following examples:

• plot_construction.cpp --> ??
• biharmonic3_example.cpp -->biharmonic_planar_example.cpp
• biharmonic2_surface_example.cpp -->biharmonic_surface_example.cpp
• strongCoupling_Error_example.cpp --> kirchhoff-love_multipatch_example.cpp (replaces strongCoupling_example.cpp as well)
• strongCoupling_ALM_example.cpp --> kirchhoff-love_multipatch_post-buckling_example.cpp
• strongCoupling_Modal_example.cpp --> kirchhoff-love_multipatch_vibration_example.cpp

[hverhelst]

Moved biharmonic_surface_example to a separate issue (#17 ).
plotConstruction.cpp stays for the moment