Allow connect to remote gdbserver from command line

Make it easier to connect to a gdbserver on a remote target. You can not specify to connect to `target_ip:port`. You always have to use the drop down list. The command line arguments always look for a local program.

It would be nice to use something like `gdbgui --target target_ip:port`.

I have tried adding the target remote to a gdb script that I use.
```
target remote 192.168.42.225:1323
```
The downside to this is that gdbgui doesn't stop at main but at (for me) `_dlstart`. It also mandates creating a gdb init script so the command line would be something like:
`gdbgui -g $GDB --gdb-args "-ix gdb_script"`.