Start proxy

[garrytrinder]

Now that we can detect dev proxy installations, we should provide an easy way to start dev proxy from within VS code when a config file is in the active window.

There are a couple of ways we could achieve this

• Add a code lens to the top of the editor
• Add a command to the status bar

Either of these approaches should open a visible terminal and start the dev proxy process using the config file. To stop the proxy, users would issue Ctrl + C as normal in the terminal window.