Added an EditorConfig file

See http://editorconfig.org/

.editorconfig

@@ -0,0 +1,21 @@
+# This file is for unifying the coding style for different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[**.py]
+indent_style = tab
+
+[src/octoprint/static/js/app/**.js]
+indent_style = space
+indent_size = 4
+
+[.travis.yml]
+indent_style = space
+indent_size = 2