Ensure `/node_modules` is present prior to starting Evidence dev server

[RandomFractals]

• Add this check to startServer(url) in src/commands/server.ts
• And display Install Dependencies prompt if no nodejs modules are installed
• Include this in v1.1.0 enhancements release (#65)

[RandomFractals]

@archiewood to test:

• Create an empty project folder and open it in vscode
• Use new New Evidence Project command from the Command Palette... to start new Evidence project
• Confirm display project folder, which is the same at your open workspace folder in this case
• Open Evidence markdown document
• Click Preview to view that document page rendered by the Evidence dev server
• You should get a prompt to Install Dependencies first
• Click Yes to Install Dependencies
• Click Preview of the open Evidence markdown document again
• You should see Evidence dev server starting
• Switch to Output to view Evidence Outoup and logged commands and page pings
• You should see server generating content for the requested page being pinged
• Eventually the page should load or just click reload after you see all the query/data parts finished in the terminal output by the Evidence dev server run.

I believe this is one of the scenarios you tested last week and ended up with npm install and start server running in sequence without prompts. This should be resolved now.

If you do more testing today, please provide test steps/action as I did in this example.

All of the described workflow from above is captured in this demo gif: