add preference for EndNote MIME type stealing feature

[simon]

Scholar can now register itself as a handler for the MIME types EndNote uses to provide downloadable citations, so that clicking a "download to EndNote" link will instead load a citation into Scholar. The preference controlling this feature is extensions.scholar.parseEndNoteMIMETypes (Scholar.Prefs.get("parseEndNoteMIMETypes")). If this preference is changed, Scholar.Ingester.MIMEHandler.init() should be called to register/unregister the handler.

[david]

(In [445]) Closes #172, add preference for EndNote MIME type stealing feature
Addresses #169, add OpenURL interface hooks
Addresses #170, Put "Link" option before "Import" in drop-down menu

Fixes some advanced search flaws (there are still bugs)