add settings for replace tab.

src/options.html

@@ -35,6 +35,11 @@
 			Preserve last written code
 		</label>
 
+		<label>
+			<input type="checkbox" name="replaceNewTab">
+			Replace new tab page
+		</label>
+
 		<div id="js-status" class="status">&nbsp;</div>
 		<button id="js-save-btn" class="btn">Save</button>
 	</form>