fixed #387 : Rename asset tab

Renaming the asset name on click of asset tab
This is an interesting case.  I guess if the user tries to rename an asset to an existing asset name, we have two choices: 
* reject the rename and show the asset with that name (as you've chosen here), or
* ask the user if they want to replace the existing asset
I'm leaning slightly toward the second choice, but I hadn't really considered it.