make story views sub-states of story, added ui dropdown for tags

views were made into sub-states to allow for transitions between
them, as well as for code organization.

tag feature:

dropdown button currently does nothing, but will contain a set of
all of the tags the user has given to his/her stories. the idea with
tags is to provide a flexible implementation of a 'category' system.
with tags, users can give stories more than one, and then filter out
their stories by tag instead of just by public and private.