Make the run_queue a signal

Right now the run_queue set up in the UI is just a reference being updated in various functions, it would be better (and easier in view of #8 ) to make it a signal so when "Run" is pressed the correct queue is run.

Start in the UI code that sets up run_queue and trace the functions that currently update the reference, then follow the Run action to see how the queue is selected. The change is complete when run_queue is a signal and pressing Run causes the correct queue to run; no specific files or tests are named in the issue.

Written by the indexing model from the issue text.