Collections 4 / MODX3: add option to use the template picker for creating a new child #340

Would be nice to use the allow the template picker to be used for creating collection children.

Probably should be optional as for some containers you'll want it to always use the same template, but when there are multiple options the template picker is nice.

(Also kinda related to modxcms/revolution#16004, which is currently preventing the creation new documents in Collections.)