Allow declaration of requirements in script manifests.

[drobbins]

For example:

{
    "name" : "TCGA Scraper",
    "description" : "Scrapes the directory structure of the TCGA into an RDF graph",
    "url" : "https://raw.github.com/drobbins/TCGApps/master/Scraper/tcgascraper.js",
    "dependencies" : [
        "http://example.com/dep1.js",
        "http://example.com/dep4.js"
    ]
}

would load http://example.com/dep1.js and http://example.com/dep4.js before loading TCGA scraper.