Allow macros to opt-out from WYSIWYG quick actions

Note that this would also be useful for macros that are meant to be internal.
All the ones we use for Notification Administration have their own quickaction. The `example` macro from the Help module has its own quickaction despite being documented nowhere...

From what I understand, we should probably create the command `xwiki-macro-hidden` that are not shown in the quickactions at any point.