core: i18n refactoring:

- _() is no more installed in __builtin__
    - instead, there is a new sat.core.i18n module
    - added D_() method for deferred translation
    - languageSwitch method allow to dynamically change translation language
    - import gettext is tested against ImportError, and dummy methods are used when not available (mainly useful for Libervia)

src/plugins/plugin_misc_text_syntaxes.py

@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from sat.core.i18n import _, D_
 from logging import debug, info, error, warning
 
 from wokkel import disco, pubsub
@@ -28,7 +29,7 @@ from lxml.html import clean
 import re
 
 
-CATEGORY = "Composition"
+CATEGORY = D_("Composition")
 NAME = "Syntax"
 _SYNTAX_XHTML = "XHTML"
 _SYNTAX_CURRENT = "@CURRENT@"
@@ -85,7 +86,7 @@ class TextSyntaxes(object):
 
     params_data = {
         'category_name': CATEGORY,
-        'category_label': _(CATEGORY), #FIXME: check that gettext can handle this
+        'category_label': _(CATEGORY),
         'name': NAME,
         'label': _(NAME),
         'default': _SYNTAX_XHTML,