feat: update pricing of domains

[Th0rgal]

We decided to update domain prices because short domains are not very popular. Here is what it will look like:
5+ letters keep their price (about $25-30)
4 letters will cost 50% less, around $40
3 letters will cost 20% less, around $180
2 letters keep their price
1 letters will cost 50% less, so around $600

This pull request performs this prices update. In ETH prices (approximately):
5+ letters = 0.009 eth/year
4 letters = 0.013 eth/year
3 letters = 0.0584 eth/year
2 letters = 0.24 eth/year
1 letter = 0.195 eth/year

closes #24

[irisdv]

lgtm