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This minor releases adds two new concepts (:star: :star:) that also exist in the KE-chain backend. We added a `Banner` concept that allows powerusers
to set an announcement banner which is displayed (and can be dismissed) in KE-chain for all logged-in users within a certain timeperiod. We also added the concept of a `Notification` in KE-chain, where email or in-app notification can be displayed suchs as sharing a link of
a task to another user, or sharing a PDF of a task to another user or and external email address.
* :star: Implemented `Banner` model and methods to create, delete and retrieve them. 725 (Thanks to jelleboersma for the implementation)
* :star: Added the concept of a `Notification` including the possibility to retrieve, create(send) and delete `Notifications`. 467 (thanks to raduiordache for the implementation)
* :star: Added the possibility to share a link or PDF of an activity using the `Activity2.share_pdf()` or `Activity2.share_link()`. 467 (thanks to raduiordache for the implementation)
* :bug: When adding a new `Activity2` to a parent, it will now cache its childeren in case the parent also have the children cached. In essence it updates the `_cached_children`. 722 (thanks to jelleboersma)
* :+1: dependent versions for development: pytest (5.4.1), mypy (0.770), tox (3.14.6)