Set up CI that builds all examples on Linux

[knatten]

Refer to https://github.com/zivid/zivid-python and do it the same way

[nedrebo]

Zivid officially support Ubuntu 16.04 and 18.04, both those should be covered.

However, the additional distributions tested against in zivid-python is probably overkill and for this and will only result in maintenance overhead.

[knatten]

It's probably a good idea to also check that samples with missing dependencies build when the dependency is turned off. For instance setting OpenCV_DIR to a non existing directory and USE_OPENCV=OFF should work.
This will reveal if we add a sample to CMakeLists.txt without adding it to the proper dependency lists.

(Idea came from #23 (comment))

[knatten]

Should build on both Ubuntu 18.04 and 16.04.

[knatten]

We're building on Linux in CI. I've added #42 and #43 to improve further.