I think the error means that the way to load library in your code is not acceptable anymore in mx7. Dojo.provide and dojo.require is old way. You can check the boilerplate of widget as example to do those things.
Hi,
A lot of app store widgets use jQuery so i would try to copy their approach.
If i look at the HTML snippet for example https://github.com/mendix/HTMLSnippet/blob/master/src/HTMLSnippet/widget/HTMLSnippet.js
var scriptNode = document.createElement("script"),
scriptNode.type = "text/javascript";
scriptNode.src = //jquery path
domConstruct.place(scriptNode, this.domNode, "only");
Hope this helps,
Andrej
Check the DragAndDrop support widget in the AppStore. It has the jquery UI library implemented as well: