Add experimental .clang-format
This adds a configuration file for clang-format  and a test file to demonstrate benefits and current problems with respect to Qt Creator's coding rules . This is based on clang-format from the llvm/clang 5.0 branch, which is about to be released soon in the next days/weeks (already behind schedule). Using clang-format for Qt Creator brings these advantages: * Enforce a bunch of coding rules by a simple tool/shortcut invocation. * Spend less review cycles for authors and reviewers regarding formatting. This helps especially for/with first-time contributors. * clang-format sorts includes and using declarations. * clang-format adds/updates namespace end comments, e.g.: } // namespace Foo See dist/clangformat/README.md for setup instructions und currently known issues.  https://clang.llvm.org/docs/ClangFormat.html  https://doc-snapshots.qt.io/qtcreator-extending/coding-style.html Task-number: QTCREATORBUG-17643 Change-Id: I87bdd66b8e492e99a360022962b00...