The "global" action constants (the ones previously in `actions.js`)
have been moved to a separate module. This was necessary to avoid a
circular dependency in an upcoming change that was causing problems.
In general the "ducks" pattern of organizing Redux stores does result
in circular dependency problems. This is because reuse of actions
between reducers is encouraged, so it's not uncommon for two reducers
to want to reference an action from the other. Going forward we can
avoid this problem by moving action constants that are shared between
reducers into this shared module.
