UnconstrainedTimeIndexedProblem: exposed write-able properties do not check validity or update dependent variables

[wxmerkt]

The exposed write-able properties Q, H, W, Q_rate, H_rate, W_rate should be made private and exposed via getters/setters to a) check validity (dimensionality of matrices or value range) and b) update dependent variables (e.g. a change of X_rate should update X).

Left to do as of June 2018:

• [ ] W (should check dimension before setting)
• [x] W_rate (should update W by multiplying)

[VladimirIvan]

Q, H, Q_rate, H_rate have been removed in #245.