Oasis: Update user's storage from back-end more often

Under the old UI, the storage usage number above the grain list updated more proactively than it does under the new UI. I think I had designed it to query for an update every time the user visited the grain list. (The storage usage number stored in Mongo can be stale -- the backend has the right number, but does not publish it reactively, so it needs to be queried from time to time.)
