Issue GetDKAN/dkan#2759: workflow emails changes

[dharizza]

connects /issues/2759

Improvements for text in workflow moderation state change emails.

[janette]

@stefaniefgray I've removed references to Page and Blog content since page content is not handled by the workbench interface (only site managers can create/edit) and blog content does not exist in OOB dkan.

Data story is also not configured to be run through the workbench UI but I think that is a separate issue.

[janette]

@stefaniefgray I noticed a problem with the instructions for where to find the "My workbench" link and I've updated the email text, can you update the docs

https://dkan.readthedocs.io/en/latest/components/workflow.html

When logged in as a user that has been assigned a Workbench role, the “My Workbench” button will be displayed on the site’s main navigation toolbar.

should be

When logged in as a user that has been assigned a Workbench role, the “My Workbench” button will be displayed in the administration menu at the top.