Rewrite tooltips to vanilla JS

[aschempp]

The new implementation should behave and look exactly the same, but has some subtle but useful improvements:

• it only ever uses one DOM element for all tips, and that element is much simpler (just a DIV with text content). Previously every tip (once used) created its own DOM element wich consisted of multiple DIVs.
• it keeps the title attribute on elements, until these are focussed by mouse pointer. I would assume this is better for accessibility.
• It automatically updates to any changes of the title attribute (or the tip content) since it is retrieved whenever the element is mouse-hovered. That's also why we don't need Backend.retrieveInteractiveHelp anymore before copying an element in wizards.
• It automatically hides the tip when clicking button or links, therefore we don't need Backend.hideInteractiveHelp anymore. This was previously only the case for buttons, but now also magically works e.g. for our module wizard in layouts. 😎

It is (currently) not supported for developers to add their own tips (= register their own element for tips). But since the core automatically uses tips for basically anything with a title attribute, I don't think that's really necessary.

[leofeyer]

Did you test that this also works with subpalettes that are loaded via Ajax?

[aschempp]

Did you test that this also works with subpalettes that are loaded via Ajax?

yes, that's why we use the MutationObserver 😎