Cashtab does not parse parameters from an address nor does it remove them if they are present. However, it does validate for cashAddr format.
In its current state, Cashtab will throw a validation error after scanning a QR code with parameters.
This diff (1) Removes any scanned parameters from the address when entered into the 'to' field and
(2) parses for an amount param, and passes it to the amount field (Send BCHA screen only).
Its designed to work with mercurymessenger.io, which uses the prefix ecash: and satoshis after the amount param.