Migrate to dkc-next being live in production

[mgrauer]

This is a tracking ticket to cover moving data.kitware.com to the dkcnext stack. It should be broken out into a milestone with individual tasks, once the tasks become more clear.

• migrate the data (The Great Migration #170 is a start)
• migrate users/permissions/groups, which will involve a lot of filtering and mapping
• decide on a path to migrate user/passwords
• any oauth providers?
• how to link kitware users with users, retire kitware users on employee exit, and associated data policies
• create data admin tools, so we can see where all the space is going (an api endpoint of top level folders sorted by size is sufficient)
• have anonymous upload working
• have hashsum download tested and working for ITK examples and test data (Matt McCormick), Pulse data (Aaron Bray)
• filter data as part of moving
• outreach to people
• what api endpoints/clients do we need to support existing demos backed by DKC
• user docs