Provide a simple way to package together a wiki macro and the pickers needed for its parameters

As a wiki macro developer I want to be able to:

1. implement a picker for a macro parameter using only wiki pages (JSX, SSX)
2. associate the picker to the macro parameter from the wiki
3. package the picker together with the wiki macro so that users installing it can use the picker when inserting the macro from the WYSIWYG editor

ATM we have this:

1. in order to implement the picker I need to have a custom skin where I can define my custom HTML displayer template. See XWIKI-15827. This is not good because I can't force my users to use a custom skin in order to have the picker.
2. in order to associate the picker to the macro parameter I need an existing Java type (class). I can use some existing type that is not related to my macro but it's a hack (e.g. "java.lang.StringBuilder") hoping that no one else will use the same type..
3. I can package the custom skin but I can't ask the users to use it