Catalogs can now be renamed by double clicking them in the Asset
Browser. This is mostly done through the tree-view API, the asset
specific code is very little.
There is some polish left to be done here, e.g. the double click
currently also collapses/uncollapses and activates the clicked item. And
the rename button takes the full width of the row. But addressing these
is better done as part of some other behavioral changes that are planned
anyway.
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