Interpreter selection should show folder name instead of venv

[qubitron]

Environment data

• VS Code version: 1.22.0
• Extension version (available under the Extensions sidebar): 2018.3.1
• OS and version: Windows 10
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv

Actual behavior

Selecting a virtual environment as the active interpreter shows Python 3.6.4 (venv) in the status bar

Expected behavior

The folder name for the virtual environment should be used instead, so that you can differentiate between different environments, e.g. Python 3.6.4 (mydevenv)

Steps to reproduce:

1. Select a virtual environment as the active interpreter

CC @DonJayamanne @brettcannon

[vincentzlt]

same here but on Mac with vscode version 2018.3.1 and virtrualenv

[DonJayamanne]

Closing this in favor of #1351, as that's where the display formats were discussed to great length.