Replace global gulp dependency with npm scripts

Isolates the build from the developers global environment so if gulp
radically changes it's API in a future version, builds will still work.
Extend default state on first DB fetch

Ensures that any state items (like "drafts") that are not in the initial
DB fetch are still included in the component state.
Set empty obj into state rather than null

If the app attempts to find the current sprint, but one is not
available, setting a null value into the state caused the Sprint
component to crash.
Add empty sprints array to initial App state

This should have been included in 82d2dd2, when the Sprint model was
added.