Fixes the following in RegisterXamlComponentRecursive method (called for example on Paste):

- Getting the correct namescope for RootItem (the INameScope case was not checked).

- Clears the local namescope for the object if it exists, otherwise name changes will be registered in the local namespace instead of RootItem document namespace.

- Only adds _Copy (or CopyX, where X is an integer) if the previous name did not already end with _Copy. This prevents names as "myname_Copy_Copy_Copy..." to occur when copying and pasting already copied elements.

- Registers the new name to the RootItem namescope, only setting site.Name is not enough as its not yet a part of the RootItem document namescope.
Added test for testing generated names for pasted element copies and that the new names is registered in the correct namescope.
Merge pull request #71 from gumme/NamescopeFixes

Fixed namescope problems in WPF Designer