Add flag for RAWBITS to use raw bits with DAALA_EC.

The use of raw bits is now disabled by default and can be turned on with:
 ./configure --enable-experimental --enable-rawbits
This commit has a negligible impact on rate.

subset1:

master@2017-02-14T18:57:22.282Z -> no_rawbits@2017-02-14T18:57:41.977Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0000 | -0.0000 | -0.0000 |  -0.0000 | -0.0000 | -0.0000 |    -0.0000

objective-1-fast:

master@2017-02-14T18:52:48.425Z -> no_rawbits@2017-02-14T18:52:04.489Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0001 | -0.0001 | -0.0001 |  -0.0001 | -0.0001 | -0.0001 |    -0.0001

Change-Id: I01e79e9f314565a64b224ca41047f7bd7fe33f70