get_trace locks out trace1, returns in remote mode

[mgiustina]

After using get_trace, the PNA is left in a state that is tricky to use locally/manually.

1. Suppose get_trace has been used to get a signal that the PNA identifies as trace2. Afterward, it is no longer possible to manually activate trace1; one must manually delete trace1 (even if it wasn't in use before) and then manually activate it again.

2. After calling get_trace in the PNA server, the PNA is left in remote mode. This is not critical, but it would be nice to save the user the regular button-pressing needed to switch back to local mode.