Add a season feature

[Sarrus1]

These changes add a "Season" feature:

The database now has 3 tables:

• rankme (same structure as the previous version)
• rankme_season (same structure as rankme with an additional column: season_id
• rankme_season_id (contains season_id with start and end dates)

Stats are tracked globally like on the previous version, but in addition they are also tracked by season, just like if you would reset the rankme table every season.

I don't know if this is in the scope of the project.

Please feel free to contact me for any question or requests.