Add support for generating diagrams from workflows.

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

mayan/apps/document_states/widgets.py

@@ -1,6 +1,8 @@
 from __future__ import unicode_literals
 
-from django.utils.html import format_html_join
+from django import forms
+from django.urls import reverse
+from django.utils.html import format_html_join, mark_safe
 
 
 def widget_transition_events(transition):
@@ -11,3 +13,23 @@ def widget_transition_events(transition):
             ) for transition_trigger in transition.trigger_events.all()
         )
     )
+
+
+def widget_workflow_diagram(workflow):
+    return mark_safe(
+        '<img class="img-responsive" src="{}">'.format(
+            reverse('document_states:workflow_image', args=(workflow.pk,))
+        )
+    )
+
+
+class WorkflowImageWidget(forms.widgets.Widget):
+    def render(self, name, value, attrs=None):
+        final_attrs = self.build_attrs(attrs)
+
+        if value:
+            output = []
+            output.append(widget_workflow_diagram(value))
+            return mark_safe(''.join(output))
+        else:
+            return ''