Sprint/Meeting are not associated with other sprints/meeting or a larger events

[Laura Czajkowski]

Sprints/Meetings are not associated with a group of sprints, or a larger sprint.

Steps to reproduce:

* Log onto https://launchpad.net/sprints/+new
* Fill in the information
* There is no way to associate this event to a series of events, or a large group of event

Use Case 1:

Mario would like to organsie a series of sprints to focus on a series of features for an application.
He registers for sprints/meetings different dates but they are all grouped through a tag that indicates the focus of the sprint

Use Case 2:

Documentation team organises a global documentation effort sprint
The team creates the general sprint and global cordinators can associate local instances of that meeting to their respective local team.