Move babel config out of setup.py.

Use the setup as shown here:
https://github.com/mauritsvanrees/maurits.i18ntalk/blob/master/talk.rst

extract.ini

@@ -0,0 +1,7 @@
+[lingua_python: **.py]
+
+[lingua_xml: **pt]
+
+[lingua_xml: **.xml]
+
+[lingua_zcml: **.zcml]

setup.cfg

@@ -5,11 +5,13 @@ directory = plone/dexterity/locales
 statistics = true
 
 [extract_messages]
+mapping_file = extract.ini
 copyright_holder = Plone foundation
 output_file = plone/dexterity/locales/plone.dexterity.pot
 msgid_bugs_address = dexterity-development@googlegroups.com
 width = 80
 charset = UTF-8
+sort_output = true
 
 [init_catalog]
 domain = plone.dexterity

setup.py

@@ -22,10 +22,6 @@ setup(name='plone.dexterity',
       packages=find_packages(exclude=['ez_setup']),
       namespace_packages=['plone'],
       include_package_data=True,
-      message_extractors = {"plone": [
-            ("**.py",    "chameleon_python", None),
-            ("**.pt"  ,  "chameleon_xml", None),
-            ]},
       zip_safe=False,
       install_requires=[
           # 'Acquisition',