Nested Attribute Code Smells with PT/PL/MP

[alexauritt]

There seems to be some needless hackery here.

1. There was a bug for ProblemLevel#new -- we were previously unable to add a problem level to an empty ProblemType. The current fix is to explicitly build a new problem level for the problem type (@problem_level.problem_type.problem_levels.build) in ProblemLevel#create. Shouldn't be necessary, but without it, we get a ProblemType can't be blank error, even through level.problem_type reference seems fine.

2. ProblemType currently expliclity initializes problem levels. ( before_validation :initialize_problem_levels, :on => :create, in ProblemType model.) Seems like this shouldn't be necessary.

[alexauritt]

Issue #2 seems to be fixed. But we're still building (@problem_level.problem_type.problem_levels.build) in ProblemLevel#create