Remove use of transaction and add filter in event admin

• Removed the use of a transaction wrapping event processing, as this was causing very long-running transactions for some projects. This shouldn't have a significant impact and error reporting via the logging module should be relied upon.
• Added a "processed OK" filter to the event admin (thanks @myles)

Fix bug in ticket admin search

v2.0.2

Bump micro version for bugfix

Fix handling of priority to cope with null values from Zendesk

Some tickets have an undefined priority, which was not being handled properly.

Adding support for Django3 and dropping support for Python2

Adding support for Django3 and dropping support for Python2

Store Zendesk user alias

v1.4.0

Bump version for 1.4.0 release

Add support for Zendesk authored comments

Zendesk authors comments with a special user with ID -1. This update allows Zengo to sync comments made by this special user.

Handle absurdly long attachment file names

Attachment file names are embedded in the Attachment.content_url field value as a query parameter. For long file names, this was causing the value to exceed the 200 chars default max_length of URLField, and in turn, was breaking event processing. Since this data only ever comes from Zendesk's API, it is "trusted" - for this reason I opted to remove any max_length restriction for the field.

Add support for attachments

Store details of Attachments associated with Comments. No content is downloaded.

Sync users and comments in consistent order to avoid deadlock

Avoid deadlock by syncing users and comments in a consistent order (#3)

* Avoid deadlock by syncing users and comments in a consistent order

* Avoid overwriting `created` result from Ticket `update_or_create`

* Reinstate and improve tests for comment syncing

* Bump version

Add basic admin and model __str__ methods

Add basic admin and model __str__ methods (#2)

* Add basic admin and model __str__ methods

* Bump version number