Move explorer to Azure viewContainer

[Loghorn]

See microsoft/vscode-azuretools#167

This will move the IoT Hub Devices explorer to the Azure viewContainer, along with others Azure plugins.

[formulahendry]

Hi @Loghorn , thanks for your PR. 😃 However, if we move the IoT Hub Devices explorer to the Azure viewContainer, users may have more context switch between the devices and files. So I'd like to keep this PR open for more discussion and user feedback.

[Loghorn]

Sure, I understand.
I proposed the change for consistency with the other azure extensions, but you are right that this could end in more context switch.

[hammar]

I didn't notice this PR and just submitted the duplicate #542 that does more or less the exact same thing (though it adds a dependency on another Azure extension, rather than redefines the Azure view container locally). Sorry!

For the discussion on context switching you bring up: I (and, I assume, many other devs) use VS Code for a variety of tasks, some of which are within the Azure ecosystem, and some of which are not. It is definitely jarring to have Azure things pop up outside of the Azure view container; that itself is more of a context switch for me. So a vote from me as a user is to merge this PR.