renaming task#sort_order to task#position,
removing project#sort_order, and adding a new
join table to handle sort order per project per user.
adding 'acts_as_list' gem
added some arrows for use in reordering items.
Big ol' honkin' commit. I ripped out the three-way
relationship between users, roles, and projects.
Now a user has_many projects, and a project belongs_to
a single user. This simplification was necessary
because I wanted to use the acts_as_list gem to
provide support for re-ordering tasks and projects,
and acts_as_list wouldn't work with the ternary
relationship without a lot of effort.

The simplification was *justified* because, let's be
honest, no one but me is ever going to use this
To Do app. There is one such app per developer
per framework.

Projects and tasks are now re-orderable.