Implement "Season" class

[RamParameswaran]

Description of feature/enhancement

• create a "Season" module/class. This class is a kind of container, which holds all information about active teams and players that season.
• the relevant data is scraped from https://afltables.com/afl/stats/1998.html

Description of implementation

• Init function takes arg: "year" (int). for example: s = Season(1999)
• class attributes:
  1. s.teams - returns a list of Team objects which were active in this season
  2. s.players - returns a list of Player objects who were active this season
  3. s.statistics - returns a single Pandas dataframe with all Team season totals tables concatenated into one dataframe
  4. s.url - URL for the season (the argument provided in the init method)

Additional context

• where possible, dataframe records should have relational links to other model instances (e.g. Player or Team) and URLs (for programmatic scraping of nested pages)

[RamParameswaran]

This may not be necessary anymore due to Team.season_stat(year) classmethod in the Team model.

Although, maybe there is a use-case for querying the entire AFL by season, rather than querying just one team ... Thoughts welcome..!

[RamParameswaran]

Closed by PR #13