Add functionality that verifies first-party domains

[alicerunsonfedora]

Thus far, SEAlice can determine that an applet's identifier is valid if it is able to load the domain and not receive a 404 error (this may need some polishing). However, there should be a system in place to determine the following:

• Whether the domain is first-party
• Whether the applet with said domain is an actual applet from a first-party