Update project files for XCode 4.6 on Mac OS 10.8
CPXYGraph initWithFrame: needs an explicit cast in release mode

The existing code builds fine in Debug mode but fails in Release. Casting
NSRect to CGRect (which have identical layouts in memory) fixes the issue.
Ignore XCode project files
Add support for time zone offsets

FlySight normally names files and sets modification times using UTC. This
changeset adds a TZ_Offset configuration value, allowing the user to work
in local time.

The logged data retains the same format, e.g. "2013-09-04T02:02:39.50Z",
regardless of TZ_Offset, but this way a day's worth of skydives will be
stored in the same directory and with filesystem timestamps suitable for
correlating with video files or other captured data.
Add Dir_format config option, supporting YYYYMMDD naming convention