Added the final bit of functionality to the search: limiting searches to particular image annotation categories:

• Added a JavaScript function to ensure that when an annotation category is selected, then "Gravure" is selected as the document type, since it's the only type of document that does contain annotations.
• Added another function to ensure that when a document type other than "Gravure" is selected, the annotation category selector is set to blank. Thus it should be impossible to search for annotation categories without limiting the document type to Gravure.
• Added annotation category handling to the find.xq file which does the XQuery search. This entailed changes to the BuildSearchStringBit function, since that's the best place to handle it. There are two new scenarios to handle: when there's both a search string and a category constraint, in which case it has to search only within annotations in that category, and when there's no search string but there is a category constraint, in which case it just needs to retrieve a list of documents which contain annotations in that category.

Minimal testing so far, but it seems to be doing the job OK.