added attributes to frontend entity model

src/public/javascripts/entities/attribute.js

@@ -0,0 +1,34 @@
+class Attribute {
+    constructor(treeCache, row) {
+        this.treeCache = treeCache;
+        /** @param {string} attributeId */
+        this.attributeId = row.attributeId;
+        /** @param {string} noteId */
+        this.noteId = row.noteId;
+        /** @param {string} type */
+        this.type = row.type;
+        /** @param {string} name */
+        this.name = row.name;
+        /** @param {string} value */
+        this.value = row.value;
+        /** @param {int} position */
+        this.position = row.position;
+        /** @param {boolean} isInheritable */
+        this.isInheritable = row.isInheritable;
+        /** @param {boolean} isDeleted */
+        this.isDeleted = row.isDeleted;
+        /** @param {string} dateCreated */
+        this.dateCreated = row.dateCreated;
+        /** @param {string} dateModified */
+        this.dateModified = row.dateModified;
+    }
+
+    /** @returns {NoteShort} */
+    async getNote() {
+        return await this.treeCache.getNote(this.noteId);
+    }
+
+    get toString() {
+        return `Attribute(attributeId=${this.attributeId}, type=${this.type}, name=${this.name})`;
+    }
+}