feat: Fail on launcher-, reporter-, or preprocessor-load errors.

Fail out of karma if a launcher, reporter, or preprocessor fails to
load, after attempting to load each of them, and reporting errors for
each load error.

**This is a WIP**: I can't quite figure out where to place a final check on
whether any errors were caught while loading launchers, reporters, or
preprocessors. Any quick tip would be much appreciated!

Closes #855