Feature request: Proof parameter verification progress

[karalabe]

When lotus is downloading the proof parameters, there's a nice progress bar. Could the same be added for verification purposes too? Given that it's about 100GB in total, it takes a while to read through them (especially when running off an HDD (testing)). Would be really nice ti know what the progress is.

E.g. lotus-miner run will spend ages reading these files on startup