Move template sandbox to its own app

Improve UI for the sandbox template textarea.

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

mayan/apps/templating/forms.py

@@ -0,0 +1,30 @@
+from __future__ import absolute_import, unicode_literals
+
+from django import forms
+from django.utils.translation import ugettext_lazy as _
+
+from .fields import TemplateField
+
+
+class DocumentTemplateSandboxForm(forms.Form):
+    result = forms.CharField(
+        help_text=_('Resulting text from the evaluated template.'),
+        label=_('Result'), required=False, widget=forms.widgets.Textarea(
+            attrs={'readonly': 'readonly', 'rows': 5}
+        )
+    )
+
+    def __init__(self, *args, **kwargs):
+        self.model = kwargs.pop('model')
+        self.model_variable = kwargs.pop('model_variable')
+        super(DocumentTemplateSandboxForm, self).__init__(*args, **kwargs)
+        self.fields['template'] = TemplateField(
+            help_text=_(
+                'The template string to be evaluated. '
+                'Use Django\'s default templating language '
+                '(https://docs.djangoproject.com/en/1.11/ref/templates/builtins/)'
+            ), label=_('Template'), model=self.model,
+            model_variable=self.model_variable, required=False
+        )
+        self.order_fields(field_order=('template', 'result'))
+        self.fields['template'].widget.attrs['model'] = self.model