Cmake add version and soversion

[cdluminate]

Changed CMake files in order to add SONAME for libcaffe.so.

Adding SONAME would be convenient for Distribution maintainers to maintain a package.

This patch is derived from debian packaging repo of caffe.

Please have a look at it, thanks.

[lukeyeager]

I would like to see all of these things together in one patch:

1. Mark v1.0 (Use the semantic versioning and add a version header file #486)
2. CMake builds the lib with an SONAME (this)
3. Make builds the lib with an SONAME (example: NVIDIA@18a3ff4)
4. build/tools/caffe --version returns the version (caffe --version should print the version/git hash #2969)
5. pycaffe.__version__ returns the version
6. Something similar for matcaffe

I started working on this but had to abandon it for something else. Feel free to steal some of this if anything is helpful:
master...lukeyeager:cmake-versioning

[lukeyeager]

Also, you could update the summary to print the version:
https://github.com/BVLC/caffe/blob/9a244f9bcf/cmake/Summary.cmake#L77

[shelhamer]

Thanks for submitting this @cdluminate but let's focus on the complete patch by @lukeyeager in #3311.