Add .editorconfig rules and fix some indents (#462)

.editorconfig

@@ -0,0 +1,32 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.md]
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = false
+
+[*.{yaml,yml,yml.dist,yml.tmpl}]
+indent_style = space
+indent_size = 2
+
+[Makefile]
+indent_style = tab
+indent_size = 4
+
+[Dockerfile]
+indent_style = space
+indent_size = 2
+
+[*.{sh,bats}]
+indent_style = space
+indent_size = 2
+
+[target/start-mailserver.sh]
+indent_style = tab
+indent_size = 4