Improve gitignore

[Siedlerchr]

I noticed that the .gitignore entry for mac's DS_Store is wrong (the leading slash must be removed) and I suggest to add a couple of more things to the gitignore files:

I suggest using an auto generated one from gitignore.io that covers nearly all use possible temp files:

https://www.toptal.com/developers/gitignore/api/linux,macos,windows,intellij,eclipse

[dlemmermann]

Done, added, thank you!