Update cabinets and document_index api views docstrings. Update multi level docstrings as per Python best practices.

Signed-off-by: Michael Price <loneviking72@gmail.com>

mayan/apps/checkouts/handlers.py

@@ -9,7 +9,6 @@ def check_new_version_creation(sender, instance, **kwargs):
     """
     Make sure that new version creation is allowed for this document
     """
-
     NewVersionBlock = apps.get_model(
         app_label='checkouts', model_name='NewVersionBlock'
     )

mayan/apps/checkouts/widgets.py

@@ -14,7 +14,6 @@ class SplitTimeDeltaWidget(forms.widgets.MultiWidget):
     A Widget that splits a timedelta input into three <input type="text">
     boxes.
     """
-
     def __init__(self, attrs=None):
         widgets = (
             forms.widgets.NumberInput(