minor modifications to conform the existing code to the new data structure

major issues: (i) for choice-set without the scale alternative, s11 should not be scaled but
read from theta (ii) the case of 2 choices is tricky because (a) n.maxChoice - 1 = 1 thus
squeeze will not work and (b) no draws are needed

- ProbitProb: squeeze() does not work for the case of 2 choices, use permute() instead
- LogLike: use dataR.pick to pick up neccessary values for d_nLogLike
- ConstructParams: depends on the size of theta, determine whether s11 is scaled to 1 or
to be read from theta
- ConstructDaraGroup: (i) recode the alternatives for each choice-set group so that we
have consecutive code 1, 2, ... (ii) record whether s11 need to be scaled or to be read
from theta (iii) in the case of 2 choices --> no draws are needed