Properly pass token+amount param combo

"scanning a request that has tokenid (c parameter) and amount (f parameter) specified just allows me to enter a BCH amount. This is not really desired behavior if I have a QR-code that specifically requests say 1.99 in MUSD and then when scanned the wallet just ignores it and allows the user to enter a BCH amount. Paytaca handles this correctly and also doesn’t let me send anything if I don’t have that particular token in my wallet."

This should also work for pasted strings. When token amount & category is specified, pass that into the send screen.

Background reading: https://bitcoincashresearch.org/t/bip21-query-parameters-for-cashtokens/1015

Follow up ticket: #644