Check for recommended langauge extension, prompt for installation

[sriv]

With just gauge-vscode installed, the user can author specs and implement them. However, language features (for implementation) is not available until the language extension is installed.

Javascript support is shipped by default in Visual Studio Code.

Detect the language of the project and suggest recommendation so that VSCode can report issues/pass feedback fast.

Some recommendations:

	"java":   "vscjava.vscode-java-pack",
	"dotnet": "ms-dotnettools.csharp",
	"python": "ms-python.python",
	"ruby":   "rebornix.ruby",