Created "reset settings" button.

As mentioned in #151

_locales/de/messages.json

@@ -500,5 +500,22 @@
 	"exportSettings_label": {
 		"message": "Anzeigen",
 		"description": ""
+	},
+	
+	"resetSettings_title": {
+		"message": "Einstellungen zurücksetzen",
+		"description": ""
+	},
+	"resetSettings_description": {
+		"message": "",
+		"description": ""
+	},
+	"resetSettings_label": {
+		"message": "Zurücksetzen",
+		"description": ""
+	},
+	"resetSettings_confirm": {
+		"message": "Sind Sie sicher, dass Sie alle Einstellungen zurücksetzen wollen?",
+		"description": ""
 	}
 }

_locales/en/messages.json

@@ -504,5 +504,22 @@
 	"exportSettings_label": {
 		"message": "Show",
 		"description": ""
+	},
+
+	"resetSettings_title": {
+		"message": "Reset settings",
+		"description": ""
+	},
+	"resetSettings_description": {
+		"message": "",
+		"description": ""
+	},
+	"resetSettings_label": {
+		"message": "Reset",
+		"description": ""
+	},
+	"resetSettings_confirm": {
+		"message": "Are you sure you want to reset all settings?",
+		"description": ""
 	}
 }

options/options.js

@@ -26,6 +26,11 @@
 		exportSettings: function(){
 			logging.verbose("open settings export");
 			window.open("export.html", "_blank");
+		},
+		resetSettings: function(){
+			if (window.confirm(browser.i18n.getMessage("resetSettings_confirm"))){
+				browser.storage.local.clear();
+			}
 		}
 	};
 	

options/settingsDisplay.js

@@ -263,6 +263,12 @@
 			"displayDependencies": {
 				"displayAdvancedSettings": [true]
 			}
+		},
+		{
+			"name": "resetSettings",
+			"displayDependencies": {
+				"displayAdvancedSettings": [true]
+			}
 		}
 	];