This temporarily disallows connections from and to the same element
because it rendered the connection unusable..
This change can be reverted once proper auto layout for circular connections is implemented.
Closes#176
It is now possible to add bendpoints to flows or drag bendpoints to
update their position / trigger reconnects.
Upon bendpoint move a rule is checked to figure out whether or not a
bendpoint operation is allowed or not.
Closes#123Closes#138Closes#139Closes#165
