Add NetlistTraversalDecorator

[julianspeith]

• added NetlistTraversalDecorator to the HAL core to collect all functions traversing the netlist and returning some set of gates depending on the specified conditions in one place
• moved some functions from netlist_utils (old ones now deprecated)
• old functions still used, e.g., in the GUI, will need some cleanup in the future
• get_(shortest_)path and get_(complex_)gate_chain functions must still be moved