Modified hash rate calculations

[mining-visualizer]

I tried to break things into different commits ... I don't know if it makes it easier for you or not

Summary of changes:

• there were a couple of bugs in formatHashRate()
  • expressions like 10e3, 10e6 & 10e9 should have been 1e3, 1e6 & 1e9
  • The Math.round function only takes 1 parameter, so I added a new round() function
• Changed the way hash rates were being estimated. Instead of averaging the hash rate associated with each share, it now sums up the difficulty of each share, and calculates a hash rate based on that.
• Eliminated the hash rate column in the Submitted Share list on the Profile page.
• Formatted the hash rate value at the top of the Profile page