ENH: Add functions for File entities

For https://gitlab.indiscale.com/caosdb/customers/cfaed/management/-/issues/29. This introduce a specific treatment of file entities and some other helper functions. This MR also introduces the retrieval with multiple ids.

Test together with f-inline-references branch of complexity wiki (use server profile in local-inline-references). npm pack this repo, then npm install it in the complexitywiki and start the react app. Verify that the functionality introduced here (files, Property.isList, and multi-ID retrieve) work as expected.

src/Entity.js

@@ -53,6 +53,14 @@ export class Entity {
         return this.wrappedEntity.getDescription();
     }
 
+    getFilePath() {
+        if (!this.isFile()) {
+            throw `Only FILE entities can have a file path.`;
+        }
+        const fileDescriptor = this.wrappedEntity.getFileDescriptor();
+        return fileDescriptor.getPath();
+    }
+
     getId() {
         return this.wrappedEntity.getId();
     }
@@ -90,4 +98,8 @@ export class Entity {
     isRecord() {
         return this.wrappedEntity.getRole() === api.v1.EntityRole.ENTITY_ROLE_RECORD;
     }
+
+    isFile() {
+        return this.wrappedEntity.getRole() === api.v1.EntityRole.ENTITY_ROLE_FILE;
+    }
 }