Make fragment system more plugin-ish

[Kukks]

• Introduce new yml properties:

plugin:
    description: "This is a description of the docker plugin"
    name: "An amazing service integrated into the BCTPay Server deployment service"

• Remove hardcoded routes in NGINX for services and introduce them in each relevant fragment
• Create a script that can go through all fragments and document all available plugins/fragments inside README file (instead of the current hardcoded descriptions)

We can then show these options in the BTCPay UI and allow users to install these options without SSH