Node group sockets have user-exposed data types, and sometimes
subtypes for some data types (e.g. Percentage or Angle for floats).
The UI to select these types and subtypes use an operator menu with a
text depending on the current type or subtype.
This button needs to be manually translated since its label is
manually defined.
Additionally, some subtypes need to be extracted from the Property
class's RNA_ENUM_PROPERTY_SUBTYPE_NUMBER_ITEMS, so this commit also
removes Property from the extraction blacklist in
bl_extract_messages.py. This has the side effect that it introduces a
few dozens translations, which are probably not used anywhere.
Damien Picard