Add animation to sweep progress bars with bootstrap class. Resolves #77.

Summary of changes:
 * Changes #sweep_progress_bar view helper by adding different classes to element depending on the number of pending sweeps.  If pending sweeps are 0, (and the sweep is completed), then the class doesn't have animated stripes.
 * Adds 2 new specs to check that class is being appropriately applied depending on the number of pending sweeps.
 * All specs passing.