Team creation view

[Mateusz-Dobrzynski]

TO-DO:
Make a view for team creation at /t/{tournament_id}/teams/create containing:

• A form with inputs corresponding to all team parameters;
• A "Create" button causing a POST /team request to be sent to backend. Upon success, a toast message is displayed (similarly to [98] "Copy motion" button debate-tools#103). The form gets cleared out, allowing further team creation;
• A "Back" button taking the user to /t/{tournament_id}/teams;
• The view is only available to people with a WriteTeams permission. Upon entry, a check is made and in case of a lacking permission, 403 error page is displayed.

How to test:

• Create a team. Ensure that:
  • The team was created in the database,
  • The form is cleared out,
  • A toast message appears.
• Enter the subpage URL as a user without the permission. Expect a 403 error.