[TYPO3-core] make the tree collapsable

[Martin Kutschker]

Steffen Kamper schrieb:
> 
> there are a lot of issues that has to be fixed without t3skin.

But some things still don't work in t3skin:

Missing icons (mostly "flagged" versions of tables, eg when the record 
is in a special state). "Broken" borders around checkboxes. Weird 
"border system" in many admin-only tools.

etc

Anyway, what I want to so is that we have a skinning system. So stuff 
should work with both skins and possibly with 3rd party skins as well.

Masi