make gnc_path_get_localedir() and GETTEXT_PACKAGE available for python
to access locales. Import gettext module to provide _ as translator
method. Provide null _-method returning english text in case of missing gettext.
Make a lot of messages translatable by adding _-method. Include python
files to create .pot-files.
Note core-utils.i is used by both the guile and the python bindings so
it is moved up to the common bindings directory, while guile
specific changes are in bindings/guile.
