Assign UUID to Sessions

Creates sessions with a UUID.
Use UUID when creating session via web

Creating or selecting a session redirects to include
"?session=${session.UUID}" in the URL.
Search Sessions by UUID

Swaps the SessionId in Votes from using the Session.Id to Session.UUID.
Swap long for Guid as Session.Id

Drops the Session.UUID, and sets Session.Id as a Guid type.
Force new session Id

EntityFramework does not auto-assign GUIDs to new sessions, so we do it
ourselves.
Add return-key hook for new session

Triggers the "Create session" task when return is pressed inside the
"Create session" input field.
Merge pull request #21 from tpkelly/feature/anonymous-polls

Anonymous poll urls