Migrate some of the graphs from index.nav.community

[reilg]

Details from email:

Migrate some of the graphs from https://index.nav.community/stats.html (which is not updated anymore):

> “Amount of staking coins considering addresses active in the last
day”

  — This chart shows the total stakable balance in every address which
had one stake in the last 24 hours.
  — In average, every 30 seconds there is a new block in the Navcoin
blockchain. Therefor, look up needs to go 2880 blocks in the past.

  ~~ Hot Staking is a category used for addresses with a spendable
balance that matches its stakable balance.
  ~~ Cold Staking is a category used for addresses with 0 spendable
balance and equal stakable balance and voting weight.
  ~~ Cold Staking v2 is a category used for addresses with 0 spendable
balance and voting weight, but greater than 0 stakeable balance.
  ~~ Combined is a sum of the previous categories.

> “Total spendable supply”

  — This is the evolution of the total Nav in Circulation (as shown in
the current main page)

[ ! ] All the graphs should show data from the genesis block (height 0).
[ ! ] Each graph should describe how the shown data is calculated.