57adde4be6
This reverts commit bf30024dd7, because
it breaks EMailFormatter/Parser extensions, like the prefer-plain.
The thing is that the internal formatters/parsers (also extensions)
should be always added first, and only after then can be added extended
extensions, which are used before those internal. This constraint was not
satisfied with the reverted commit, the order of extension registration
was unpredictable, depended on GType.