Accept URLs as an argument to CLI "download" command

CLI Download command requires passing arguments like exercism download --exercise=pal-picker --track=common-lisp. Arguments --exercise and --track are not convenient to type, so the only option is copy and paste from the “work locally” field:

This field has a number of usability issues on my Linux system with xterm. This field does not display the whole command in a way that I can select it and paste into xterm with a middle click. I can only copy it into the clipboard, while xterm uses the cut buffer by default. I can work around the issue by configuring UXTerm*selectToClipboard: true or using a clipboard manager. It can also be considered an issue of the web interface that only the part exercism download --exercise=pal-pick can be selected.

However, this topic is not about the usability of the “Work locally (via CLI)” field. I propose a simpler interface: let the command
exercism download
do the same as
exercism download --exercise=pal-picker --track=common-lisp.

The browser URL bar uses common OS controls and you can expect that copying and pasting URLs from the browser to the terminal works reliably in any environment, even if it is about copy-pasting the URL from Firefox for Android to Termux.

This interface is also well known to GitHub users. It has a dedicated interface, and it is useful especially if you want to clone over SSH:
But git clone (the URL displayed at the top of the browser window) works as well if you simply want to clone the repository in a read-only mode.