started support for local storage in apps

Ignore-this: ded07bcbea3569daf747654ddb8173fd

added new disk store class to store data on disk. The design is simple, data
is stored in a dictionary. Each piece of data has a uuid which is mapped to a
human friendly key. The value is stored on disk as a seperate file using the uuid
as the file name. By providing this kind of proxy, you can save on disk and use "disk paths"
as keys without causing safety issues. Currently no limit in storage.

The lua api will provide set and get functions for this data.

There are two kinds of app data, local data, and app data.
App data is transfered to others while the local data stays local.

darcs-hash:20140128062827-c21fe-e189d983bccf63ef272f63b5d8d15f31d3e83511
updated util README to reflect new files

Ignore-this: a29cfce56a78162fdf31dbdd6e7d2ac8

darcs-hash:20140128063552-c21fe-e810791fa42260895069be418887e83ef2361b3b