Fix issue with lowercasing in datatypes/registry.py

[remimarenco]

Hi :),

I was working on changing my USCS Track Hub datatype extension and I had the (ironic) good idea to put uppercase in it.

Exceptions inside registry.py, about a KeyError. I saw that in the load_datatypes function, there is a lowercasing handling of extension name, but it does not appear then in load_display_applications.

I added the lowercasing in this last one, added a log.debug message to prevent the user it could generate issues later on, and refactored it to follow DRY.

Let me know what you think about it :)

[jmchilton]

@galaxybot test this

[remimarenco]

Yay all tests passed!

[nsoranzo]

👍

[dannon]

Thanks @remimarenco!