Add Command line Arguments to gtkwave call

[tkrawuts]

To automatically load a safe file when an external gtkwave window is executed during simulation the following command line option should be added:

--save ./gtkwave_config.gtkw

To be more flexible it would be of great value to configure the command line of the gtkwave call in e.g. "project settings"

[Miresker]

With #170 the command line arguments for the GTKWave call can be configured with the burger menu in the testbench.