Calculated columns now integrated in search result

* dataresult table extended for calculated columns
* "calc" and "calculate" allowed as keywords for calc columns in AugQL

expression improvements:
* restricted function set now allowed in python expressions (currently
  only math functions (-> checked by WhiteListExprVisitor))
* allow some more nodes like Pow or BoolOp (Or, And, ...)

other:
* more and better expression parsing / compiling testing
* much faster get_entries functions