Don't try to build translations for .py and .ui source files

They don't exist any longer.
Fixed concurrent update of component details dialog

We accidentally created a new rate limiter on each event, because the
constructor call was being only partially applied. Fixed API to avoid
the same mistake in future.

Error was:

(0install:6487): Gtk-WARNING **: Invalid text buffer iterator: either the iterator is uninitialized, or the characters/pixbufs/widgets in the buffer have been modified since the iterator was created.