Gracefully handle unsupported browsers

[will123195]

Unhandled promise rejection 
Object { name: "TransportError", message: "U2F browser support is needed for Ledger. Please use Chrome, Opera or Firefox with a U2F extension. Also make sure you're on an HTTPS connection", stack: "TransportError@https://localhost:8000/dist/LedgerSDK.js:1779:16\n[5]</</TransportU2F.listen/<@https://localhost:8000/dist/LedgerSDK.js:1631:22\nrun@https://localhost:8000/dist/LedgerSDK.js:6768:22\nnotify/<@https://localhost:8000/dist/LedgerSDK.js:6786:7\nflush@https://localhost:8000/dist/LedgerSDK.js:5831:9\n", id: "U2FNotSupported" }