Additional options (no due date, priority)

[evandavey]

Would be useful to include the following additional options:

• include where the due date has not been set
• filter on priority

This would allow emails functionality:

• send all users an email showing their work pipeline - issues with no due date + issues due in x days
• send all users an email showing their 'x' priority pipeline (eg: send high priority alerts once a day, low priority once a week etc.)