- Unbreak the three broken tutorials (fixes#848)
- This involved a rewrite of PPP-01-10 because I already had my own
solution to that one and I couldn't easily tell what was going
wrong with the previous solution.
- Add assertions to all the tutorials so that non-raising means success
- Add the TTT examples to `test_examples.py` added recently for #909
- Also added sympy to development dependencies since one of the TTT
examples uses it.
Now generates correct model and calculates correct mass.
(note that trapezoid requires it's width input field to be calculated using angles because it's not given)
