Fangraphs and Spotrac Team Data Functions

[camdenk]

• Adapted the existing fg_*_leaders() functions to pull from the team-level data, rather than the individual players. In doing so, I also removed a few of the columns that wouldn't apply to this dataset (playerid, Name, Age).
• Added a sptrc_team_active_payroll() function to return contract data for players on a MLB team's payroll in a given year and a sptrc_league_payrolls() function to return a quick look at payrolls for the entirety of MLB