Parse scaling list from SPS

This is required for the dimensions to be calcuated properly when
streaming using the high profile (at least for the encoder I'm
using). Without this, the scaling list isn't skipped over and
the parsed dimensions are incorrect.

When the dimensions are incorrect, the MPEG-DASH manifest is
generated incorrectly.

Without the patch headers are parsed as:
```
2014/09/02 16:15:08 [debug] 11256#0: *77 codec: avc header 17000000000164001fffe100456764001fad84010c20086100430802184010c200861004308021ce5014016ec04400003e90000ea60180000039387000008583b3fffe30000007270e000010b0767fffc68001000468fe3cb0
2014/09/02 16:15:08 [debug] 11256#0: *77 codec: avc header profile=100, compat=0, level=31, nal_bytes=4, ref_frames=66, width=128, height=2144
```

With this patch:
```
2014/09/08 08:56:36 [debug] 24539#0: *4 codec: avc header 17000000000164001fffe100456764001fad84010c20086100430802184010c200861004308021ce5014016ec04400003e90000ea60180000039387000008583b3fffe30000007270e000010b0767fffc68001000468fe3cb0
2014/09/08 08:56:36 [debug] 24539#0: *4 codec: avc header profile=100, compat=0, level=31, nal_bytes=4, ref_frames=4, width=1280, height=720
```

(Note that the input bytes are identical in both cases.)