Replace all instances of unicode only handling to use force_text.

Replace all __unicode__ methods to __str__ and the
@python_2_unicode_compatible decorator.
Replace all instance of smart_str, smart_unicode, force_uncode
with force_text.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/dynamic_search/classes.py

@@ -6,6 +6,7 @@ import re
 
 from django.apps import apps
 from django.db.models import Q
+from django.utils.encoding import force_text
 from django.utils.module_loading import import_string
 from django.utils.translation import ugettext as _
 
@@ -220,7 +221,7 @@ class SearchModel(object):
 
             result_set = result_set | model_result_set
 
-        elapsed_time = unicode(
+        elapsed_time = force_text(
             datetime.datetime.now() - start_time
         ).split(':')[2]