Refactor the model accesors

Refactor the accesors to behave like methods instead of properties.
This means all accesors will be prepended with the string
"get_" and will include a set of parenthesis.

Improve the ModeAttribute class to use the method's
short_description. This commit also adds support for a
new method .help_text attribute has been added.

Move accessors to their own module, named "methods.py".

Remove the PropertyHelper class as the accessors no longer
need it.

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

mayan/apps/document_states/methods.py

@@ -0,0 +1,15 @@
+from __future__ import unicode_literals
+
+from django.utils.translation import ugettext_lazy as _
+
+
+def method_get_workflow(self, name):
+    return self.workflows.get(workflow__internal_name=name)
+
+
+method_get_workflow.short_description = _(
+    'get_workflow(< workflow internal name >)'
+)
+method_get_workflow.help_text = _(
+    'Return the current state of the selected workflow.'
+)