#261: suite database: record suite broadcast settings

Solution for #261.

While perhaps not the prettiest of solutions, the pickle string(s) that was being dumped out for suite broadcast settings is now recorded in a new table in the suite database.

Entries are timestamped (servertime) so it is possible to see what was being used at a time/changed.

For purposes of potential future changes to cylc with restarts using the database, the last entry in the broadcast states could be queried and unpickled as done presently.