Use URL instead of base64-encoded payload for deep link

[esune]

When proof-requests grow in size, the resulting deep-link can grow to over 2048 characters, causing the payload to be truncated when sent over to BC Wallet (2048 characters is the size limit for URLs) which will then fail to process the request as the decoded output is a malformed JSON.

One way to fix this would be to use a URL/shortened URL instead of the base64 encoded presentation-request, but we are unsure on whether this will work out-of-the-box or not (attempts seem to indicate this will not work as-is).

@jleach @cvarjao does a change need to get into BC Wallet to handle this, or are we maybe using the bcwallet://...?c_i=https://my-url.com (or similar OOB) syntax incorrectly with the url?