Choco API's: Support for total progress bar and cancellation

[tapika]

If choco downloads and/or installs multiple packages, there should be mechanism to observe total percentage, not only for local file.

chocolatey\infrastructure.app\nuget\NugetCommon.cs
packageDownloader.ProgressAvailable += (sender, e) =>

this event mechanism observes download progress of one file.

=> Need to have support for multiple files

Also at the moment choco does not provide mechanism for end-user to be able to cancel the download or install operation gracefully - newer API should support it.

src\chocolatey\infrastructure\commands\Execute.cs
var cancelToken = new CancellationTokenSource();

=> This should be centralized, and provided to end-user of API.

[tapika]

Potentially will solve this issue: #619

I've tested by myself cancellation, and for download it works ok, but for installation powershell exit is long waiting operation. Not sure if it's a problem, as it might be difficult to stop install process in overall.

[tapika]

Not sure how difficult would be to have built-in WPF UI, which can be activated over command line prompt, for example using --gui option.

[tapika]

To allow total progress bar to be estimated, I needed to harvest recursively all packages to get list of packages to be processed.

I suspect it should be default operation.

It allows to encounter problematic / missing package and stop operation before performing anything.

This is useful in case if you downloading 3 packages, and one of them is missing from server.

Potentially can fix issue: #1521

[tapika]

Can potentially solve this issue: #701