Avoid using minDFA dimensions unless necessary

[zivnevo]

Using minDFA incurs performance penalty. We should try to avoid using it, unless necessary.

For example, consider a containment query asking whether the allowed connections of network-config A are contained in those of network-config B. If the allowed connections of B have no minDFA dimensions, there is no point in considering these dimensions when computing the allowed connections of A (because they can only refine the set of allowed connections).

We should probably have a flag to control whether or not to compute minDFA dimensions, and so we need to do it lazely, and store the results separately. Hence, this issue depends on #106.