Implement DRGx Exchange #1272

[abdul]

• What is the purpose of this Pull Request?
  A: Implements DRGx Exchange

• What is the related issue for this Pull Request (if this PR fixes issue, prepend with "Fixes" or "Closes")?
  A: Closes Implement DRGx Exchange #1272

• [✓] I have added Specs

• [✓] (If implementing Market Ticker) I have verified that the volume refers to BASE

• [✓ ] (If implementing Market Ticker) I have verified that the base and target is assigned correctly

• [✓] I have implemented the trade_page_url method that links to the exchange page with the base and target passed in. If not available, enter the root domain of the exchange website.

• [✓] I have verified at least ONE ticker volume matches volume shown on the trading page (use script below)

client = Cryptoexchange::Client.new
pairs = client.pairs 'drgx'
tickers = pairs.map do |p| client.ticker p end
sorted_tickers = tickers.sort_by do |t| t.volume end.reverse