Add .clang-format configuration file for source code formatting.

I went through every option in http://clang.llvm.org/docs/ClangFormatStyleOptions.html and picked the ones that seemed most consistent and sane.

I set ColumnLimit to 0 for now ("none") but do we want to set a line length limit? 80? 100? I know some people are pretty pedantic about this - we especially are in the Qt project :) - but personally I don't mind.

After we agree on a style and merge this we can auto format the codebase (minus third party code like bsdiff). It really is horrendous!