Logical node types: created makeLogicNode, LogicOr, LogicAnd
Logical node types: created makeLogicNode, LogicOr, LogicAnd

A function makeLogicNode(string) receives a string such as 
"AND {foo, NOT OR{ bar, baz }}" and returns a logical node
with class either LogicOr or LogicAnd (both inherit from class
LogicNode). 

'Union' is interpreted as 'OR'
enochd/RMG-Py,nickvandewiele/RMG-Py,KEHANG/RMG-Py,nyee/RMG-Py,chatelak/RMG-Py,pierrelb/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py,faribas/RMG-Py