Rootstock: Resume Swaps Percentage

[kilrau]

As a follow up of #1182: we are curently showing Scan % which quickly goes to 100%, but then is followed by preimage derivation which takes a decent time too with the progress seemingly "stuck" at 100%.

Proposal: Either go to 99% and only to 100% when preimage derivation is done OR change button message to Searching for resumable swaps...