Add information on loaded plugins

[philipstarkey]

Original report (archived issue) by Lars Kohfahl (Bitbucket: lkohfahl, GitHub: lakodarmstadt).

---

When implementing the latest progress_bar changes I stumpled over some problems with our own progress bar because I had the naming in the labconfig file wrong. However this was not noticable as labscript just silently included the new progress bar and did not inform me about the plugins that could not be loaded.
I tried to write some lines to face this problem, which probably need some improvements before starting a PR.

[https://bitbucket-archive.labscriptsuite.org/#!/lkohfahl/blacs/commits/1c7d683103d6dea218de4eedd25020f7c78b5544 (labscript-suite-bitbucket-archive/lkohfahl-blacs--forked-from--labscript_suite-blacs@27ece19)](Link URL)

[philipstarkey]

Original comment by Philip Starkey (Bitbucket: philipstarkey, GitHub: philipstarkey).

---

Good idea! Generating a notification in the GUI would be good, as well as logging to the BLACS log file. Unsure if you can generate Notifications outside of a plugin... there's probably a way to do it though!

[philipstarkey]

Original comment by Chris Billington (Bitbucket: cbillington, GitHub: chrisjbillington).

---

Failed plugin instantiation I think is in the log file already. I think I recently added a change to make it a full traceback, it used to be a bit silent.

We're saying promote this failure to a notification?