Update TemplateField to concatenate help texts

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

HISTORY.rst

@@ -9,6 +9,7 @@
 - Unify the creation of the temporary config file used in tests.
 - Update all 0001 setting migrations to not accept manually migrated
   settings.
+- Update TemplateField to concatenate existing help texts.
 
 3.3.4 (2019-12-09)
 ==================

mayan/apps/templating/fields.py

@@ -1,7 +1,7 @@
 from __future__ import absolute_import, unicode_literals
 
 from django import forms
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import string_concat, ugettext_lazy as _
 
 import mayan
 
@@ -14,11 +14,15 @@ class TemplateField(forms.CharField):
     def __init__(self, *args, **kwargs):
         self.model = kwargs.pop('model')
         self.model_variable = kwargs.pop('model_variable')
+        self.initial_help_text = kwargs.pop('initial_help_text', '')
         super(TemplateField, self).__init__(*args, **kwargs)
-        self.help_text = _(
-            'The template string to be evaluated. '
-            'Use Django\'s default templating language '
-            '(https://docs.djangoproject.com/en/%(django_version)s/ref/templates/builtins/)'
-        ) % {'django_version': mayan.__django_version__}
+        self.help_text = string_concat(
+            self.initial_help_text, ' ',
+            _(
+                'The template string to be evaluated. '
+                'Use Django\'s default templating language '
+                '(https://docs.djangoproject.com/en/%(django_version)s/ref/templates/builtins/)'
+            ) % {'django_version': mayan.__django_version__}
+        )
         self.widget.attrs['model'] = self.model
         self.widget.attrs['data-model-variable'] = self.model_variable