Change Historian to retain oldest history when items are dropped.
Add ability to exit to broadcast.

Historian understands a special history entry, 'broadcast'. This is used to indicate
that TAL should exit to broadcast rather than using the standard exit() functionality.
Add additional tests for broadcast Historian semantics
Refactor hasHistory() for clarity
Add device test for default exitToBroadcast() implementation
Add broadcast exit strategies for Samsung and LG
Add LG exit strategy
Amend LG 2013 Midrange TV to use new broadcast/widget page exit strategies.
Merge pull request #52 from fmtvp/exit-to-broadcast

Exit to broadcast