Provide jinja2 urlencode filter

Astonishingly, the great jinja2 does not provide a builtin urlquote filter,
although it is obviously needed. (jina1 had one) This is:
pallets/jinja#17

Provide an urlencode filter, based on werkzeug's url_quote_plus function.
This is dead easy to implement and gives us all the freedom we want.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

mediagoblin/tools/template.py

@@ -17,6 +17,8 @@
 from math import ceil
 import jinja2
 from babel.localedata import exists
+from werkzeug.urls import url_quote_plus
+
 from mediagoblin import mg_globals
 from mediagoblin import messages
 from mediagoblin.tools import common
@@ -62,6 +64,8 @@ def get_jinja_env(template_loader, locale):
     template_env.globals['app_config'] = mg_globals.app_config
     template_env.globals['global_config'] = mg_globals.global_config
 
+    template_env.filters['urlencode'] = url_quote_plus
+
     if exists(locale):
         SETUP_JINJA_ENVS[locale] = template_env