SEO fixes #620 & #661

Bug #620 SEO Metadata Enhancement
http://mrccodereview.cloudapp.net/ui#review:id=1259
Metadata was added to each page created by crawler.aspx

Bug #661 SEO: Add alt attributes to media tags
http://mrccodereview.cloudapp.net/ui#review:id=1260
When the crawler.aspx page generates code for an exhibit or contentItem and links to external media, the tag should include an alt attribute the same as the contentItem it represents.