Add workaround to properly display overflowing child elements of panes

[rbtbar]

The workaround preserves the initial 'auto' z-index of 'panes', so that
it is possible to keep many overflowing child elements of 'panes'
visible in front of all other 'panes' while the mouse is neither over
the 'pane' or its children;

Actually, this solution replaces handing of z-indexes via:
allowOverflow( elem_or_pane )
resetOverflow( elem_or_pane )
showOverflowOnHover
... in most of the standard use cases.

[rbtbar]

The corresponding Gist file:

https://gist.github.com/rbtbar/bfe6ddbab441bee840a2

[melloware]

Can you clean up this commit? It looks like you touched a lot of lines but made no actual changes to those lines. Did you run it through some code formatter or something?

[GedMarc]

Looks like this is already in the jquery3 branch, do you need this specifically for jquery2?
(https://github.com/GedMarc/layout/blob/master/dist/layout-default.css)

[allpro]

The new commit looks fine. The extra line edits are all just trailing whitespace trimming, plus trimming one odd but of gibberish! (abcdef)

[allpro]

However the CSS commit from 2014 would BREAK many layouts. Layout dynamically adjusts element zIndexes when panes overlap ('slide'). Hard-coding a zIndex would prevent this.

The reason allowOverflow() and similar methods exist are so users can temporarily override the dynamic zIndexes in special scenarios. This cannot be a default though.

It is OK for a 'user' to hard-coded a zIndex on a pane that requires it, assuming no other pane will ever overlay it. A common example is a header that contains drop-down menus. Again, this cannot be a default.

[allpro]

The commit with changes to layout-default.css should be reverted as it would break layout. This is explained in a comment I added.