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/widgets.py

@@ -0,0 +1,37 @@
+from __future__ import absolute_import, unicode_literals
+
+from collections import OrderedDict
+
+from django import forms
+
+from mayan.apps.common.classes import ModelProperty
+from mayan.apps.common.widgets import NamedMultiWidget
+
+
+class TemplateWidget(NamedMultiWidget):
+    def __init__(self, attrs=None, **kwargs):
+        widgets = OrderedDict()
+
+        widgets['model_property'] = forms.widgets.Select()
+        widgets['template'] = forms.widgets.Textarea(
+            attrs={'rows': 5}
+        )
+        super(TemplateWidget, self).__init__(
+            widgets=widgets, attrs=attrs, **kwargs
+        )
+
+    def decompress(self, value):
+        choices = ModelProperty.get_choices_for(
+            model=self.attrs['model']
+        )
+        self.widgets['model_property'].choices = (
+            [('', '----')] + choices
+        )
+        return {
+            'model_property': None, 'template': value
+        }
+
+    def value_from_datadict(self, querydict, files, name):
+        template = querydict.get('{}_template'.format(name))
+
+        return template