Added editor config to keep with Xceed code style.

ExtendedWPFToolkitSolution/.editorconfig

@@ -0,0 +1,11 @@
+# top-most editor config file
+root = true
+
+[*.cs]
+indent_style = space
+indent_size = 2
+csharp_space_after_keywords_in_control_flow_statements = false
+csharp_space_between_parentheses = control_flow_statements,expressions,type_casts
+csharp_space_between_method_declaration_parameter_list_parentheses = true
+csharp_space_between_method_call_parameter_list_parentheses = true
+csharp_space_between_square_brackets = true