Accept Element Callbacks in caps2tacs + Adapt Mach Wing Example

[sean-engelstad]

• Made a change in the tacsAIM of ESP/CAPS (what caps2tacs is built off of) that writes out TACS Component labels. This way the user should be able to make their own element callbacks now in TACS using BDF/DAT files created from ESP/CAPS.
• Accepts element callbacks in the TacsModel clas
• Adapts Alasdair Gray's blade stiffener examples in examples/mach_tutorial_wing since we are using this for an aeroelastic benchmark case in FUNtoFEM.

[sean-engelstad]

@timryanb note sure why the unittest failed since I didn't change anything associated with that unittest

[timryanb]

@timryanb note sure why the unittest failed since I didn't change anything associated with that unittest

There seems to be an to be an ongoing issue with the eigen solver tests intermittently failing. The tests sometimes fail rarely and randomly, which makes it difficult to reproduce. I think it has to do with the random number generator used to seed the eigenvalue solver. We can try seeding it in the future to make the tests run more consistently. I'll open a separate issue/PR for this shortly, but in the meantime feel free to to continue with this PR