Fixed unit test scripts + coverage

Tried to add more apps (others break).
"preprocessors" is now populated automatically based on the tested apps.

I tried adding more apps but the others break, as some part rely on libraries loaded only on the settings page... It's still a big mess and I guess we will some day need requireJS or something similar.

Anyway, first things first: writing unit tests for the files app and improve everything gradually.

@DeepDiver1975