Fix calculation of total number of comparisons

[hardbyte]

This calculation now takes into account the use of blocking. Also because it seemed somewhat non-trivial to compute I added caching in redis.

Closes #542

[hardbyte]

This was why I'd seen a log messages saving "0 comparisons".

[wilko77]

lgtm. Did you figure out why it was sometimes showing a progress of more than 100%?

[hardbyte]

Yeah it was just a dumb 2 party assumption on my side, I was first calculating the total number of comparisons as:

For each data provider multiple the size of each block together, then sum resulting number
of comparisons in each block all together.

When the actual calculation needed to be:

for each block:
        for each **pairwise combination** of data providers in each block:
                multiply the block sizes together
        then sum number of comparisons for each block
Sum the number of comparisons in all blocks together