Fix #289 Use the correct number of sessions for the conference

This change adds the total number of time slots and the total number of tracks to the database, and uses those values in the voting pages to visualise the data with the correct number of total sessions.

After this is merged, the number of time slots and tracks will both be set to 5 in the database.

No. Only schema changes are supported in the fluent style. I don't technically require this line, but everyone would have to manually edit their databases by hand to insert this, so I included it for ease.