Feature: Feature Pane - Folder/Feature/Scenario Tree

[alistairjevans]

In the VSCode extension, there is an AutoStep icon on the left hand side, which yields the AutoStep pane.

Currently, the only thing that this displays is a basic list of features. This pane needs to become (eventually) an AutoStep test browser, not dissimilar to the populate .NET Test Explorer extension (https://marketplace.visualstudio.com/items?itemName=formulahendry.dotnet-test-explorer), in that it should have a hierarchy of features and scenarios.

For this specification, I'm saying that the listing should display a hierarchy as follows:

Folder
   Feature
      Scenario / Scenario Outline
           Scenario Outline Variations (from Examples data)

Each level of the hierarchy should have an icon appropriate to it (from the standard set, https://code.visualstudio.com/api/references/icons-in-labels).

Currently the entire tree view refreshes every time the project builds; it would be good to only update the child nodes that have actually been re-compiled/linked.

You may need https://code.visualstudio.com/api/extension-guides/tree-view#view-actions as a reference.