add reset settings option

public/_locales/en/messages.json

@@ -947,5 +947,14 @@
     },
     "openOptionsPage": {
         "message": "Open options page"
+    },
+    "resetToDefault": {
+        "message": "Reset to default"
+    },
+    "confirmResetToDefault": {
+        "message": "Are you sure you want to reset all settings to their default values? This cannot be undone."
+    },
+    "whatResetToDefault": {
+       "message": "This resets all settings to their default values." 
     }
 }

public/options/options.html

@@ -368,6 +368,14 @@
 					</div>
 				</div>
 
+				<div data-type="button-press" data-sync="resetToDefault" data-confirm-message="confirmResetToDefault">
+					<div class="option-button trigger-button">
+						__MSG_resetToDefault__
+					</div>
+	
+					<div class="small-description">__MSG_whatResetToDefault__</div>
+				</div>
+
 			</div>
 
 			<div id="advanced" class="option-group hidden">