CMake - added `runtest` and `lint` targets

Added `runtest` and `lint` targets:

`runtest`:
- depends on `caffe` target (will invoke `caffe` build if it wasn't built earlier)
- builds tests, which have been excluded from the main build
- sets up gtest filters based on CPU/GPU mode 
- runs tests with `--gtest_shuffle`

`lint`:
- runs `cpp_lint.py` on all source files and headers with the exclusion of generated `*.pb.*` files