Fix the storymap grid.

Before, some stories were being inserted into the wrong part
of the grid. This was due to an incorrect assumption that the
pos property of the epic and sprint objects accurately reflected
the actual positions of the sprints and epics on the rendered
grid.

Now, the sprint and epic data containers are arrays, and
the positions of the epics and sprints are determined in the
renderMap function.
Fix issue with story modal loading.

Before, the loadStory function grabbed a story from the
storiesList data container and modified it. Then, it
passed the modified story to the template as a context.
If a user attempted to load the same story again, an error
would be raised, because the loadStory function accesses
a modified version of the story from the previous call.

Now, the properties of the story are copied to a new context
object, and that new context object is passed to the template
instead.