Disable project requests from contributors with no activity

[flodolo]

We keep getting project requests from people poking around.

I think we should disable project requests in at least this case:

• Contributors has no activity in the locale
• The locale already has managers

We received 7 requests since the beginning of the year:

• 2 were legit and would have passed this check
• 5 would be prevented (the contributors who made them have zero contributions to this day)

[mathjazz]

/cc @Delphine @bcolsson @peiying2 for visibility.