Freeze required package versions

Additionally, point at a patched version of PyMouse on Github. The patch
solves the hang-at-import bug.
Avoid relying on FS locations of package data

Load the eye tracking cascade XML file from a package_stream rather than
a filesystem file so that we don't require running from an exploded egg
on a filesystem. Prep for possible PyApp support.
Merge pull request #4 from casebeer/feature/package-data-stream-not-filename

Feature/package data stream not filename