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.

LibGUI/GProgressBar.h

@@ -19,7 +19,12 @@ public:
     String caption() const { return m_caption; }
     void set_caption(const String& caption) { m_caption = caption; }
 
-    enum Format { NoText, Percentage, ValueSlashMax };
+    enum Format
+    {
+        NoText,
+        Percentage,
+        ValueSlashMax
+    };
     Format format() const { return m_format; }
     void set_format(Format format) { m_format = format; }