Add proper string representations to all classes

[roclark]

Describe the bug
The classes need to have a clear string representation in order to allow users to easily view what the objects represent. In many cases, this throws an error while trying to print a class.

To Reproduce

from sportsreference.fb.team import Team

team = Team('Tottenham Hotspur')

print(team)

Expected behavior
The output of printing the team object above should display useful information about the team that it represents, the ID if applicable, and the season.

Desktop (please complete the following information):

• OS: Ubuntu 18.04 (affects all)
• Sportsreference Version: 0.5.2 and top of tree