Remove MoMA::u, MoMA::v

[Banana1530]

At the very beginning, we include u and v as members of MoMA to facilitate warm-start. They are initialized to be the SVD of data matrix X, and they are updated in real time as the PG loop runs. Ideally, we want

problem = MoMA(X, lambda_u=0)
problem.solve()
arma::vec u1 = problem.u
arma::vec v1 = problem.v

problem.reset(lambda_v=0.1)
problem.solve() // warm-start
arma::vec u2 = problem.u
arma::vec v2 = problem.v

However, as the mix of BIC search and grid search comes into our design, the concept of warm-start becomes intricate. Furthermore, dependence on MoMA::u and MoMA::v as solutions to the current or last penalized SVD problem might be a gotcha.

So lets remove MoMA::u/v and let outside code (wrt to MoMA internal code) take care of warm-start.