views: translate labels and not names (#567)

So that we can install caravel on postgresql:
```
2016-06-03 17:58:05,386:ERROR:flask_appbuilder.base:
Add Permission on Menu Error: (psycopg2.ProgrammingError) can't adapt type '_LazyString'
[SQL: 'SELECT ab_view_menu.id AS ab_view_menu_id, ab_view_menu.name AS
ab_view_menu_name \nFROM ab_view_menu \nWHERE ab_view_menu.name = %(name_1)s \n
LIMIT %(param_1)s'] [parameters: {'param_1': 1, 'name_1': l'Sources'}]
```

Other that translating names should be a recipe for disaster if
you switch language.

Fix #558

caravel/views.py

@@ -312,7 +312,8 @@ def pre_update(self, db):
     "Databases",
     label=_("Databases"),
     icon="fa-database",
-    category=_("Sources"),
+    category="Sources",
+    category_label=_("Sources"),
     category_icon='fa-database',)
 
 
@@ -368,8 +369,10 @@ def post_update(self, table):
 
 appbuilder.add_view(
     TableModelView,
-    __("Tables"),
-    category=_("Sources"),
+    "Tables",
+    label=_("Tables"),
+    category="Sources",
+    category_label=_("Sources"),
     icon='fa-table',)
 
 
@@ -399,9 +402,11 @@ class DruidClusterModelView(CaravelModelView, DeleteMixin):  # noqa
 if config['DRUID_IS_ACTIVE']:
     appbuilder.add_view(
         DruidClusterModelView,
-        __("Druid Clusters"),
+        name="Druid Clusters",
+        label=_("Druid Clusters"),
         icon="fa-cubes",
-        category=_("Sources"),
+        category="Sources",
+        category_label=_("Sources"),
         category_icon='fa-database',)
 
 
@@ -447,7 +452,8 @@ def pre_update(self, obj):
 
 appbuilder.add_view(
     SliceModelView,
-    __("Slices"),
+    "Slices",
+    label=_("Slices"),
     icon="fa-bar-chart",
     category="",
     category_icon='',)
@@ -546,7 +552,8 @@ class LogModelView(CaravelModelView):
     LogModelView,
     "Action Log",
     label=_("Action Log"),
-    category=_("Security"),
+    category="Security",
+    category_label=_("Security"),
     icon="fa-list-ol")
 
 
@@ -593,6 +600,7 @@ def post_update(self, datasource):
         "Druid Datasources",
         label=_("Druid Datasources"),
         category="Sources",
+        category_label=_("Sources"),
         icon="fa-cube")
 
 
@@ -1087,6 +1095,7 @@ def welcome(self):
         "Refresh Druid Metadata",
         href='/caravel/refresh_datasources/',
         category='Sources',
+        category_label=_("Sources"),
         category_icon='fa-database',
         icon="fa-cog")
 
@@ -1104,6 +1113,7 @@ class CssTemplateModelView(CaravelModelView, DeleteMixin):
     label=_("CSS Templates"),
     icon="fa-css3",
     category="Sources",
+    category_label=_("Sources"),
     category_icon='')