Terminal Switcher should move keyboard focus

[kieferrm]

• VSCode Version: Code - Insiders 1.15.0-insider (6feff11, 2017-08-04T17:43:56.658Z)
• OS Version: Darwin x64 16.7.0

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After having used the terminal switcher for a few days, I realize that I'm always assuming that the keyboard focus moves when I change the active terminal, same what happens when using Open View from the command pallet. As it doesn't I often end up doing the wrong thing, i.e. type shell commands in the open editor, etc.

Steps to Reproduce:

1. Open two terminals and one editor
2. Put the keyboard focus in the editor
3. Use Switch active terminal to change the visible terminal
4. Start typing
   -> the editor content is being modified

Reproduces without extensions: Yes