Camera Flags - Auto Exposure, Auto White Balance, Raw Color, & Mirror

This enables toggling of a few camera flags.  Available flags are in the `freenect_flag` enum and values in `freenect_flag_value`.  Call freenect_set_flag() to enable or disable a flag.

Internally, hardware commands and register handling were split out into flags.h and flags.c.

There are two caveats with mirror:
* The IR stream cannot be mirrored (in hardware) since doing so corrupts the stream.
* Video stream is of lower quality because the Bayer decoder assumes a GB interleave but a mirrored stream has a BG interleave.

Signed-off-by: Benn Snyder <benn.snyder@gmail.com>