Include xcolor in cvpr.sty

[igkiou]

I would suggest including xcolor inside cvpr.sty.

The current template:

1. loads xcolor inside the file preamble.tex;
2. uses it inside main.tex to define a CVPR-specific color;
3. uses that color inside the recommended hyperref options.

Given that the hyperref options are meant as part of the official template recommendations, whereas preamble.tex is meant mostly for helpful or paper-specific packages and macros (in the provided example, it's for only commenting macros), I think it would be better if xcolor were included inside cvpr.sty. That way, users can use the cvpr.sty template with its recommended hyperref settings, without needing to include the preamble.tex file or load xcolor separately.

[taiya]

If you have a pull request to implement these changes, feel free to send it.
(most likely this will be for next year)