Improve the batch rename dialog

- Use the editor-defined error, warning and success colors for
  preview texts.
- Make the "Regular Expressions" option into a CheckButton
  (as it does something as soon as it's toggled) and move it out
  of the Advanced Options submenu.
- Make it clearer that the error message originates from an invalid
  regular expression.
- Clarify what the number means in the regex error message.
- Tweak some strings' casing for consistency.

(cherry picked from commit ff135065f4)

editor/rename_dialog.h

@@ -75,7 +75,7 @@ class RenameDialog : public ConfirmationDialog {
 	TabContainer *tabc_features;
 
 	CheckBox *cbut_substitute;
-	CheckBox *cbut_regex;
+	CheckButton *cbut_regex;
 	CheckBox *cbut_process;
 	CheckBox *chk_per_level_counter;