Ignore all *.user files

[podsvirov]

For example Qt Creator create CMakeLists.txt.user file with user settings.

[podsvirov]

If this PR will be merged, I will delete there changes from #1713.

[ocornut]

For example Qt Creator create CMakeLists.txt.user file with user settings.

Will merge.
It is something that applies to the examples compiled with your others?
As in, just using Qt Creator with the CMakeLists file will create the .user file?

[podsvirov]

Yes. For storage user settings Qt Creator create CMakeLists.txt.user file when work with CMake's project.
When we open examples/CMakeLists.txt in Qt Creator, he will create only one examples/CMakeListst.txt.user file.
But if we will make install ImGui project and then open standalone example project, the CMake will find installed package and Qt Creator will create new *.user file for each standalone opened example.

[podsvirov]

Thanks for merge.