merge develop into staging

• Change the on-grid continuous deployment tool to deploy the "develop" branch to the staging grid (!176 (merged))
• Avoid copying nixpkgs to the store a second time in nix-shell. (!168 (merged))
• Allow building the local grid with a clean checkout. (!171 (merged))
• Move NixOS systems tests to nixos/tests. (!173 (merged))
• Don't include vagrant in shell.nix if running in a container. (!167 (merged))
• Don't wait for cerbot before starting PaymentServer. (!170 (merged))
• Remove some out of date perl references. (!169 (merged))
• Expose all local packages as new module argument. (!163 (merged))
• Move configuration of domain and targetHost to generic locations. (!161 (merged))
• Manage access to payment metrics (!146 (merged))
• Set NIX_PATH in shellHook of shell.nix. (!162 (merged))
• Make the per-grid inline module more explicit. (!160 (merged))
• Adopt the PaymentServer Nix packaging from our nixpkgs fork and use it (!158 (merged))
• Update issue link. (!155 (merged))
• Access morph module options via config. (!156 (merged))
• Upgrade system test software and port system tests from Perl to Python (!151 (merged))
• Services Dashboard: Payments (!154 (merged))