Dropdown implementation, switch refactoring

* Various fixes

* Fix tests

* Dropdown names deduced from pin names

* Remove update callbacks

* Fix double pins issue

* return undefined if not switch

js/element/DropdownElement.js

@@ -0,0 +1,37 @@
+import DropdownTemplate from "../template/pin/DropdownTemplate.js"
+import IElement from "./IElement.js"
+
+/** @extends {IElement<Object, DropdownTemplate>} */
+export default class DropdownElement extends IElement {
+
+    static properties = {
+        ...super.properties,
+        options: {
+            type: Object,
+        },
+        selected: {
+            type: String,
+        },
+    }
+
+    constructor() {
+        super()
+        super.initialize({}, new DropdownTemplate())
+        this.options = /** @type {[String, String][]} */([])
+        this.selected = ""
+    }
+
+    /** @param {[String, String][]} options */
+    static newObject(options) {
+        const result = new DropdownElement()
+        return result
+    }
+
+    initialize() {
+        // Initialized in the constructor, this method does nothing
+    }
+
+    getValue() {
+        return this.template.getSelectedValue()
+    }
+}