add File page to move files between stores

The File page wraps a filehandle and allows for efficient moving of
files between Stores.

This is needed for the Static file app.
make sure find_files returns absolute paths

It's been a convention that all paths in Statocles are absolute,
starting with a /.
add Static app for tracking static files

The static app is used for static files like images, CSS, JavaScript, or
anything.

Fixes #22