Move Tag workflow step to end of workflow

Addresses #579
Fix workflow step URLs when story is new

When a story is new, that is, it has no story_id because it has
never been saved, ``WorkflowStepView`` should generate links like
'/build/', '/build/info/' instead of '/build/undefined/info/'.

The logic for determining when the story ID should be included
was a little wonky.

Also make sure that the "Story Info" workflow step link doesn't
work if no model has been set, that is, if the template hasn't
been selected yet.

Addresses #579
Make "Story Info" workflow step of builder accessible for new stories

The "Story Info" workflow step, that is the "/build/info/" route
should be accessible for an unsaved story.

Define an explict route handler for this case and reorder the calls
to ``route()`` so this explicit route matches before the more
generic ones.

Addresses #579