Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

LibCore/CElapsedTimer.cpp

@@ -1,6 +1,6 @@
-#include <LibCore/CElapsedTimer.h>
 #include <AK/Assertions.h>
 #include <AK/Time.h>
+#include <LibCore/CElapsedTimer.h>
 #include <sys/time.h>
 
 void CElapsedTimer::start()