Update paths to work with Package Control

[Package Control][] puts the Flatland theme inside the directory
`Packages/flatland/Theme - Flatland`.  This change modifies all of the
internal paths to use that location rather than rely on manually
installing the theme.

[Package Control]: http://wbond.net/sublime_packages/package_control
Merge pull request #35 from tswicegood/allow-package-control-install

Update paths to work with Package Control