Report reference state of PI stages in logging file during startup, add IPython console & different handling of config files

[raacampbell]

Report to the logging file the reference status of all PI stages. Skip stages labelled as "NOSTAGE". The resulting lines in the logging file look like this:

2020-07-09 15:41:00,612:INFO:MainThread:6140:mesoSPIM_Stages:src.mesoSPIM_Stages:Axis 1 (L-509.20DG10) reference status: *UNREFERENCED*
2020-07-09 15:41:00,668:INFO:MainThread:6140:mesoSPIM_Stages:src.mesoSPIM_Stages:Axis 2 (L-509.40DG10) reference status: referenced
2020-07-09 15:41:00,723:INFO:MainThread:6140:mesoSPIM_Stages:src.mesoSPIM_Stages:Axis 3 (L-509.20DG10) reference status: referenced
2020-07-09 15:41:00,779:INFO:MainThread:6140:mesoSPIM_Stages:src.mesoSPIM_Stages:Axis 4 (M-060.DG) reference status: referenced
2020-07-09 15:41:00,835:INFO:MainThread:6140:mesoSPIM_Stages:src.mesoSPIM_Stages:Axis 5 (M-406.4PD) reference status: referenced

This change aids in troubleshooting instances where a stage is not referenced.

[raacampbell]

@ffvoigt did you get a chance to look at this? I have another pull request to send for simplifying the program startup and adding an interactive console, but I didn't want to send until this one is cleared because currently they overlap.

[raacampbell]

This pull request adds two features:

1. If there is only one non-demo config file then it's loaded automatically so the software starts with no user input.
2. There is now a command line option to start mesoSPIM_control with an interactive iPython console. This helps with debugging.

[ffvoigt]

Sorry for the long delay - I really like the IPython console for debugging & the other changes. I will merge into the development branch where I collect all updates for the next release.