update the icon to be the key

[chrisdias]

The Azure Account extension has a pretty generic, color-less icon, especially as compared to the other Azure extensions:

We should update the extension to use the subscription "key" as seen in the Portal:

You can find a the subscriptions icon used by the other Azure extensions here:

https://github.com/Microsoft/vscode-azuretools/blob/master/ui/resources/azureSubscription.svg

[miguelsolorio]

Attaching the assets. We should also update the background color of the extension page to match the rest of the Azure extensions (rgb(0, 114, 198)). Here's what it should look like:

Gallery view

Extension page

Market_AzureAccount_128x.zip