Adds ability to browse to Dapr application entrypoint.

[philliphoff]

For applications that expose a port, we add an inline context command to open a browser directly to that entrypoint, saving the developer the step of typing out the path in a browser.

Note: there's no guarantee that the base endpoint is served by the application but, currently, there's no place for developers to indicate an appropriate subpath. (That will hopefully be added to the Dapr runtime in due course.)

Note: the extension also assume the application exposes an HTTP port. (It might expose a gRPC port instead but, again, the Dapr runtime doesn't provide a way to distinguish between them.)

Resolves #275