Feat/Change assign player form

[makkoli]

The assign player form needs to be improved so it can handle assigning multiple players to a single team.

Currently, the assign player form only handles assigning a single player to a single team. It would be better to use something like the Material-UI stepper component.

Step 1: Display a list of all players in the league that are not in an active season and display the players with a checkbox so all checked players can be assigned to a single team.

Step 2: Display a list of all active teams that the players can be assigned to

Step 3: Have two fields, one for jersey numbers and one for positions for each player that is about to be added to the team

Submitting will then add all players on the back to that team with their jersey number and position attributes