Provide a convenient method of adding SQL comments

[gsrohde]

Currently, updates to the database schema is effected primarily through the use of Rails migrations. This helps to ensure that different BETYdb database instances conform to the same database schema.

It is, however, desirable to have a less cumbersome method of updating database comments.

Tasks

• [x] Implement comment-editing feature.
• [x] Release new feature.
• [ ] Update documentation, including:
  • [ ] General procedure for updating comments.
  • [ ] Add to instructions for issuing a new release for the case where comments change and the comments should be propagated to other deployments.