Creating submissions (and scrimmages?) breaks when not on team

[n8kim1]

from @wflms20110333 "If you try to submit code without officially creating and being on a team, it breaks. Should probably directly disallow submissions when not on teams (official one-man team is ok).

The funny thing is, the submissions tab is not displayed when you're not on a team, but I found the link in Getting Started anyway and unintentionally caught this."

A quick fix would be to say "make sure you're on a team!" on this site, but we should def look into a more robust solution later, for example by disabling the submission button entirely too. (Making the page completely inaccessible / redirecting instantly to the homepage seems unhelpful.)

Note -- this may also apply to trying to create a scrimmage when not on a team -- need to investigate.

see battlecode/battlehack20#100

[LittleAlvinMaker]

I tested submitting a file without being on a team, and I got a "Forbidden" response. It seems that my fix is hidden behind a permissions check, which I suspect comes from the IsAuthenticatedOnTeam permission at views.py:671. Unfortunately, this means the upload fails without any visible feedback at all. Is that enough to close this issue, or is there more that needs to be done?

[n8kim1]

related: #6, #13, #69