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Market version 29
New loggers + internal changes

new loggers:
- skylines (xkylines.xcsoar.org) livetracking support
- livetrack24 (livetrack24.com) initial livetracking support
- IGC file + WXC signature support

- keep loogers' states/objects within a session:
 - less ctor/dtor cycles
 - changed the GetFileLoggers() logic (keep current list within Session)
 - add 'close()' method to be called when logging stops