Fixed undo for insertCharacters() and deleteCharacters()
Fixed undo for insertCharacters() and deleteCharacters()

corinthia/corinthia-editor,corinthia/corinthia-editor,corinthia/corinthia-editor,corinthia/corinthia-editorlib,corinthia/corinthia-editorlib,corinthia/corinthia-editor,corinthia/corinthia-editorlib,corinthia/corinthia-editorlib,corinthia/corinthia-editor,corinthia/corinthia-editorlib