broadcast: provide delete broadcast configuration feature

[Saxon Milton]

Provide a delete broadcast button to allow easy deletion of broadcast configurations (you have to do from cloud console datastore viewer otherwise); the list can get quite cluttered.

[Saxon Milton]

Merged in delete-broadcast (pull request #236)

broadcast: add broadcast delete button to broadcast page

Resolves issue #240

Approved-by: Alan Noble Approved-by: Trek Hopton

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