Reset variant when composer mode is set for a channel

When a persona is deleted, the appropriate variant set on the session remains until the session expires or the variant is changed. When the composermode is enabled for a channel the variant should be reset to default.

Meta data HEAD response after persona deletion when re-opening a channel:

Content-Type text/html;charset=UTF-8
Date Fri, 19 Oct 2012 12:48:07 GMT
HST-Mount-Id 825b6997-fb11-450f-bbb0-9e9f84852cff
HST-Page-Id fd9ff84a-9584-4c0b-a7c8-41a852820477
HST-Render-Variant consumer
HST-Site-HasPreviewConfig false
HST-Site-Id 8afd9a29-5e74-422a-9058-526c341801a1
Server Apache-Coyote/1.1
Transfer-Encoding chunked
X-HST-VERSION 2.25.05-SNAPSHOT