- re-organize calcOmega and struct to be done in a modular way (object)
- enable UN by block if and only if the user specifies repetition

Suggestion from Julie:
- for baseline adjustement use syntax like interaction(time,group, time = 3:5) so time 0:2 are constrained equal between groups (mean, variance, and correlation).
- add structure =exp= via corExp (no variance structure)
