[#1181] Correct computation of progress for Spend before Sync

[LukasKorba]

Closes #1181

• the computation of progress changed, the total range is computed, that way it works for any kind of sync algorithm
• the progress depends on finished scan action, whenever it processes some blocks, it's counted up
• the final progress is a ratio between these new values

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[HonzaR]

It looks good to me. Left only one question inline.

[HonzaR]

Just from curiosity, what are these weights used for?