Moved presentation loading to index.erb out of parade.js
Added Presentation Path Prefix

A presentation path prefix is set by the env['SCRIPT_NAME']. This
is restoring a feature that was added with the following pull
request:

https://github.com/schacon/showoff/pull/136/files

* All JS/CSS helpers will now recognize include the path prefix
* The JavaScript presentation will request the slides from the correct prefixed path
* The image paths are updated correctly as well
Allow ImagePaths to be more tolerant of nils in prefixes
Updated specs for UpdateImagePath to test presentation_path_prefix
Merge branch 'multi-tenat-hosting'
Version 0.10.1