experiments with invalid number of participants

[alee]

It is possible to create "degenerate" experiments where the number of participants and groups isn't enough to actually run the experiment properly. Should provide some level of validation to warn the user that this is occurring.

Example: creating 10 test participants for the boundary effects experiment AB/BA/AD create 3 groups, 2 with 4 participants and 1 with 2 participants. The group that doesn't get linked to a cluster will end up being degenerate and prevent the experiment from running properly.

This isn't a huge issue because the group requirements is a research protocol issue (register exact # of participants) but we should at least prevent the server side from dying or leaving the database in an inconsistent state.