feat: Implement enabling and disabling devices

test/trust_test.dart

@@ -12,6 +12,7 @@ void main() {
     // Caroline starts a chat a device from Alice
     await btbv.onNewSession(aliceJid, 1);
     expect(await btbv.isTrusted(aliceJid, 1), true);
+    expect(await btbv.isEnabled(aliceJid, 1), true);
 
     // Caroline meets with Alice and verifies her fingerprint
     await btbv.setDeviceTrust(aliceJid, 1, BTBVTrustState.verified);
@@ -21,6 +22,7 @@ void main() {
     await btbv.onNewSession(aliceJid, 2);
     expect(await btbv.isTrusted(aliceJid, 2), false);
     expect(btbv.getDeviceTrust(aliceJid, 2), BTBVTrustState.notTrusted);
+    expect(await btbv.isEnabled(aliceJid, 2), false);
 
     // Caronline starts a chat with Bob but since they live far apart, Caroline cannot
     // verify his fingerprint.
@@ -32,5 +34,7 @@ void main() {
     expect(await btbv.isTrusted(bobJid, 4), true);
     expect(btbv.getDeviceTrust(bobJid, 3), BTBVTrustState.blindTrust);
     expect(btbv.getDeviceTrust(bobJid, 4), BTBVTrustState.blindTrust);
+    expect(await btbv.isEnabled(bobJid, 3), true);
+    expect(await btbv.isEnabled(bobJid, 4), true);
   });
 }