More tests, some small bugfixes

[dellaert]

• added comprehensive tests in HybridBayesNet
• fixed a number of issues in test frameworks, equality checking, etc.
• added choose method in HGC, operator() now sugar
• made sample more aware of bad inputs
• made potentiallyPrunedComponentError a local function
• refactored printErrors -> polymorphic error works fine!

[varunagrawal]

Some major comments about Switching.h, and some nitpicks.

[dellaert]

I'd rather not do another CI so please approve and I'll make the small changes in the next PR. I think it's basically only small change.

[varunagrawal]

I am still not sure about the K values though.

[dellaert]

I am still not sure about the K values though.

K is number of variables X, K-1 modes, right?
for K=3: X(0), X(1), X(2), and M(0), M(1) i.e., modes end at K-2 = 3-2 = 1.