Participants can only have one discipline

[sjmf]

Currently with how the database is designed, a participant is assigned to a single discipline via the discipline_id foreign key field on the Participant table.

In reality, a scientist may cross over multiple disciplines, such as in the case of Biochemists (Biology and Chemistry), or Crystallographers (Chemistry and Physics). In these cases, there are issues with duplication of participants in the master sheets, where they appear more than once.

We are currently using the "ignore duplicates" option to assign a participant to their first discipline, in the order that the sheets appear in the master. However, it may be the case that in future, we will want to allow participants to be in multiple disciplines.