Refactor workflow listing

[ewels]

The code in this tool to fetch the pipeline names and releases uses the GitHub APIs. It works fine, but it was from before we had the new website. Now the website does the same calls and provides everything we need in a single JSON file which we can fetch with a single API call.

URL: http://nf-co.re/pipelines.json

Pros:

• Simpler code, faster
• No GitHub API usage limits
• We can collect usage stats in the future on the website
• Only need to maintain website, not multiple tools (eg. which repos to ignore etc)

Cons:

• None..?

Can keep the existing code as a backup if we want? Though to be honest probably easiest to strip out the GitHub stuff and keep it simple..