Open .clang-format files from prefererence/properties page

[ghentschke]

As a user I want to change the format (a.k.a. code style) settings via the .clang-format file on project or on workspace level.

Since the .clang-format file is not visible to the user by default in the project explorer, because of the filtering for .* files, the solution could be, to add an open-format-file button in the editors preference/properties page.

When there is no such file, it should be created with a default content.