Add Distribution of Block Rewards

[damcnuta]

Averages can be misleading especially with only 1 week of data. It would be helpful to view the full distribution as well as the block rewards plotted across time to visually how the distribution is changing.

[elenahoo]

To provide unbiased view, we need to plot the block profit from each block. This could be quite messy, i can use median instead of average, it'd be less mis-leading.

[gheise]

• Create graph representing the distribution of block rewards.
  Note: Use percentiles and median