Consider maintaining own master branch

[NikolausDemmel]

Goal is to include bug fixes, drop support for older versions (minimum Ubuntu 16.04, C++11, cmake 3.2 or 3.5 or something).

Some of the things to include:

• Switch to C++11 Standard and remove boost dependency JakobEngel/dso#164 and other open PRs from https://github.com/JakobEngel/dso/pulls