gdbserver COM in GroupBox is saved for consistency

Signed-off-by: Yunlu Zhang <Yunlu.Zhang@synopsys.com>

Now that Debugger plugins has several Groups of UI elements
- one for each gdbserver, TextBox used to choose configuration file for
gdbserver should be moved into this Group as well, for consistency. COM
port related source codes need to be changed for this purpose.
Fix a GUI bug on nSIM props for consistency

Signed-off-by: Yunlu Zhang <Yunlu.Zhang@synopsys.com>