Move mapController instantiation to succcess callback

mapController was being defined after the function
`getCurrentPosition` which takes a success and a
failure callback.

It's weird to define things that the callback is
dependent on *after* control is being yielded to
the callback.
Merge pull request #74 from tiger-swallowtails-2014/relocate-instantiation-of-mapController

Merging myself as per Steven, to attempt to fix heroku deployment issues.