Notification upon "New environment" or "New database version"

To include in the feature list for the notification framework (besides #230 (closed) and #227 (closed)):

• If a new database version is released by the system administrators, it should signal a search for all experiments using the previous version and notify the relevant user a newer version of the database is available (with a link to the new database page).
• If a new version of an environment is released, then we should do the same, i.e., scan all experiments that use that environment and notify users of the new environment (with a link to the new environment description).