Finish workflow context implementation

Improve workflow instance detail view.
Add workflow transition field widget support.
Fix workflow transition field required support.
Update tests.

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

mayan/apps/document_states/html_widgets.py

@@ -0,0 +1,39 @@
+from __future__ import unicode_literals
+
+from django import forms
+from django.template.loader import render_to_string
+from django.urls import reverse
+from django.utils.html import format_html_join, mark_safe
+
+
+def widget_transition_events(transition):
+    return format_html_join(
+        sep='\n', format_string='<div class="">{}</div>', args_generator=(
+            (
+                transition_trigger.event_type.label,
+            ) for transition_trigger in transition.trigger_events.all()
+        )
+    )
+
+
+def widget_workflow_diagram(workflow):
+    return mark_safe(
+        '<img class="img-responsive" src="{}" style="margin:auto;">'.format(
+            reverse(
+                viewname='document_states:workflow_image', kwargs={
+                    'pk': workflow.pk
+                }
+            )
+        )
+    )
+
+
+class WorkflowLogExtraDataWidget(object):
+    template_name = 'document_states/extra_data.html'
+
+    def render(self, name=None, value=None):
+        return render_to_string(
+            template_name=self.template_name, context={
+                'value': value
+            }
+        )