Add CMake-based build support on stable/2.11

[Mizux]

Add CMake based build + Makefile/docker CI + Travis-CI

[wolfv]

I am packaging CoinUtils up to google-or tools for conda right now and I am basing it off of your CMake files.

However, they don't seem to install a pkgconfig file, right? I think it would be nice to also configure a pkg-config file so that users of that toolchain can still use it.

[Mizux]

This patch was mainly to add Coin-OR to the CMake world (e.g. in order to consume it in google/or-tools when using the CMake build system, have a clean vcpkg package)...

Sure you can add pkg-config generation using CMake but:

1. out of the scope of this PR IMHO, could be done in a later PR
2. I'm currently not have a working business need for it, I need a Modern CMake config file to depends on it or be able to incorporate it to a super project build (see FetchContent)

[wolfv]

I understand what and why you're doing this -- but IMO this current CMake is wrong in this regard and it doesn't generate a "clean" recipe if it doesn't additionally install the pkg-config file since (especially in a package manager) other downstream packages might need / expect the file.

Btw. do you want to be part of the maintainers for the conda packages? I am adding or-tools next, just waiting for the (lib) protobuf build on conda to be based on CMake as well:

https://github.com/conda-forge/staged-recipes/pull/10935

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