[RFC] WebP image format support addition

WebP is an image format based on VP8 standard. I have implemented WebP decoder support for OpenCV. Tested decoding with one of the provided samples (samples/c/morphology.c code) and WebP image is getting decoded successfully. In coming weeks I will start working on WebP encoder.

This is just a request for comment and not a pull request as the code quality is not yet in par with OpenCV standards. It will be great if I could get comments at an early stage. I welcome any sort of comment so that the code quality can be improved and brought up to OpenCV standards.

Please note that the current code needs lot of cleanup (logging, coding style etc) and I will be doing that in parallel while implementing WebP encoder support.

Note:
1. FindWebP.cmake is not available by default in Ubuntu 12.10's repository. I am using one version taken from another project. It is not present in my commits as it is taken from a GPL'ed project.
2. I have enabled WebP support by default as I am not much aware of cmake.
3. Copyright headers are incorrect and need modifications.
In future code changes I will try to address these.