[bug] Distance functions don't load correctly after first fail

[Michaeljfang]

To reproduce error:

1. In ~/generics/DistanceFunction.py, change the return string of DisplayName() of any of the distance function classes to "NA". Suppose this is "Chi Square Distance'
2. Start app and close the "error loading modules" window.
3. Reverse the change in step 1.
4. Reload all modules by going to the canonicizers tap, pressing the right control key, and clicking the "Reload all modules" button.
5. Select "Chi Square Distance" (or whichever class was modified in step 1) from the Analysis Methods tab, and the following error is printed to the CLI:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python3.8/tkinter/__init__.py", line 1892, in __call__
    return self.func(*args)
  File "/mnt/p4s/code/Live/PyGAAP/PyGAAP_gui.py", line 1737, in <lambda>
    find_description(t, l, d), add = "+")
  File "/mnt/p4s/code/Live/PyGAAP/PyGAAP_gui.py", line 333, in find_description
    + API_dict[name].displayDescription()
KeyError: 'Chi Square Distance'