first PR for opencv integration

@nitishsrivastava,

I prepared first PR for opencv integration. There are a lot of changes, I tried to test them all and hope that I didn't break anything.
Several comments about changes:
- I removed CImg dependency from image_iterators, but it still used in extract_representation_cpu.cc & util.cc\h (class ImageDisplayer). I plan to rework them to opencv also in next PR(s).
- I completely removed dependency from tclap. The only inconsistency is that opencv CommandLineParser doesn't support multiple arguments, so I changed gpus list on --board=012... (without delimiter, but probably will be better to use some, for example, ";") and layers list onto --layer=layer1;layer2;...
- I renamed jpeg2hdf5 to image2hdf5, because opencv support different image formats.
- I found that in some files you use Apache license, so I added it in all source files, which I changed.
- I tried to update all documentations with these changes.
and this should be base2 = 2*num_pixels