Added features:
- Assignee can now be added and removed.
- Avatar icon is at card and assignee details
TODO:
- When selecting new assignee (+) icon, list does not yet show avatars and names who to add.
There is empty avatar without name.
Thanks to xet7 !
Fixes the data context on the member popover in the details pane. Also
change the way Popover detect if the click is initiated from a parent
popover -- from reading Blaze context, to looking at the event target
parents.
