Add to/fromJSON methods to State and Accounts

This is needed since all storage in manifest v3 is key-value-pair-based
and session storage of most data is actually serialized into an
encrypted string.

libs/common/src/models/domain/account-profile.spec.ts

@@ -0,0 +1,9 @@
+import { AccountProfile } from "./account";
+
+describe("AccountProfile", () => {
+  describe("fromJSON", () => {
+    it("should deserialize to an instance of itself", () => {
+      expect(AccountProfile.fromJSON({})).toBeInstanceOf(AccountProfile);
+    });
+  });
+});