Setup scheduled tasks to auto-update CC artists

[treyhunner]

There are three sources of CC artists that should be updated regularly (daily or weekly):

• Magnatune (sqlite DB download and import script)
• Jamendo (import script using API)
• Free Music Archive (import script using API)

There are Django management commands for these, but they don't have tests yet.

[macro1]

If the management commands are working, we should just set that up manually for now, till we can look into a more comprehensive deployment strategy.