fix for dropdown check selection in variables

Change-Id: If36dbbb8020751b2cc2cb91cc128939cbb2fe5c4
adds a key handler to delete components when selected in Designer

Change-Id: Ie567c46bf46e5f726890dbe702e7c2ea73900e25
Fix typeblocking and mutators.

This code fixes the problem that type blocking didn't work for blocks
with mutators and it adds a type block for 'create empty list'.

Change-Id: Icf33cd06ea5e4616808cff6da6d8c9c631138dd4