Use githubs gitignore files.

[Pfeil]

I'd prefer to use this kind of gitignore file. It uses some of the well-maintained lists from https://github.com/github/gitignore. This makes basically two changes:

• Include a lot of files we have never seen and usually will not see.
• Exclude all folders named "build" by default, with the exceptions of such folders located in /src. If a legit exception has to be added, it can be done like this: !/setup/build/env.sh but to be honest I do not expect this to happen.

I left in some things I was not able to tell where it is coming from, namely /.settings/ and /config/, so no lines or files were left out in the end.

[Pfeil]

Sorry for the force push, I thought I did not have a pull request already. But well. I almost forgot about that branch.

• modified the starting comment a little to make it hopefully a little better to understand what I mean.
• Added os specific files to avoid thumbnails and similar things to be committed.
• Added the line you proposed.

What do you think?

[Pfeil]

If this is fine, I think you'll have to merge, I think I can not ... probably that is why I forked the template repo back then :)

[Pfeil]

Merging the master has deleted the travis.yaml, still it seems to be triggered? The rest of the CI is probably fixed by #6 by then.