Add support for SEP-0007 payment requests

[ebma]

• Add transactionRequest context (to parse and store incoming SEP-0007 requests)
• Add <TransactionRequestHandler> that checks the uri stored in the transactionRequest context and shows dialogs according to its content
• Add <VerifyTrustedServiceDialog> that is shown for incoming SEP-0007 requests that have an origin_domain but are not in the list of trusted services. The user can then decide to trust this domain and it will be added to the list of trusted services.
• Add <PaymentAccountSelectionDialog> that is shown for incoming SEP-0007 pay requests. It shows details of the pay request and allows the user to select an account to use for this payment. Only accounts that hold a trustline for the specified asset will be shown in the list. A warning will be shown if the request is not signed. Selecting an account will show the payment dialog for the selected account.
• Add preselectedParams as prop to the <PaymentForm> to be able to pre-fill the respective input fields with values of the pay request. Pre-filled input fields will be disabled so that the user cannot change the value.
• Enable trusted services by default (Remove the feature flag)
• Save settings to localStorage in web build (makes it easier to test trusted services but is useful in general)

Closes #323.

Preview of the <PaymentAccountSelectionDialog> if no origin_domain and no signature are provided:

Flow when origin_domain of request is already a trusted service:

Flow when origin_domain of request is not a trusted service:

[andywer]

Great job, @ebma! 👍

I proposed a wording change and we need to re-arrange the headlines in the view a little bit – looks somewhat unbalanced right now. Otherwise really cool.

We should also think about whether it makes sense to show the "trust this origin" dialog before the user has had a chance to see the actual request. Happy to fix this as a separate issue, though. Don't think it should be blocking.

[andywer]

One thing that we can either refactor right now or we need to do it as soon as we start working on tx type requests:

It should probably rather be called TransactionRequestReviewDialog or similar and we should pass that SEP-7 URI content rendered as a grid as children prop, so we can re-use this component for the tx type URIs.

[ebma]

I suggest we postpone it until we do the tx type requests because it might be easier to restructure once we know how we handle/show tx requests.

[andywer]

Pushed one commit with a few UI adjustments. Btw, why did you prevent the max-width to be set? I thought it looked rather strange on a desktop screen. Maybe you had your reasons, but I changed that as part of my commit.

[ebma]

The noMaxWidth stems from the other dialogs that are used in the account settings. I did not pay attention on the max-width property when reusing code from those dialogs (for the sake of consistency) so it's a good thing that you noticed and changed it. 👍
I'd also propose to tackle the issue with showing the 'trust this origin' dialog later.

[ebma]

I changed it so that the <PaymentForm> is now shown inline instead of the user being redirected to the payment dialog.

The payment form will not render without an account. That's why the first account in the account selection list is preselected by default.

If no accounts are available for the network specified in the tx-request another dialog is shown instead:

[ebma]

Superseded by #1202.