add orm.User.find and orm.[Foo]Token.find

for simple get-by-name access
cookie_secret is no longer bytes

add utils.random_hex for generating a unicode object
with random hex bytes
fix inverted logic in Server.is_up()
allow resetting the database
check if spawners are running before starting new ones
enable resuming Hub state from database
update proxy with already-running users at startup
update mocking with load-from-db changes
Merge pull request #48 from minrk/resume-from-db

enable resuming Hub state from database