xqemu-manager should download xqemu for ease of use

[MayeulC]

As discussed on IM, this would greatly improve usability for first-time users, especially windows users, that are used to easy first-time setups.

That's why I would like to make it a wizard for the first xqemu run:

1. Warn the user that their MCPX and Kernel are needed for now, with two browsing fields just under it
2. Offer to download the HDD image (a browse button, with a download button next to it)
3. Offer to download xqemu. I can see a dropdown with the 10 latest artifacts or so, and a download button next to it, plus a browse button.

The wizard could accommodate other settings in the future, such as input, and console configuration (region, etc). But those three steps are the most important for first time users. Of course, the wizard would be cancellable, launchable again, pages could be skipped, and the downloaders could be called again directly from the settings.

An update check could also be performed on launch, and offer the user to upgrade if a new one is available.

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As a reference, these were my alternative proposals to make the setup easier:

• creating a repo with xqemu-manager and xqemu as submodules, that would compile both
• changing the xqemu appveyor script to include xqemu-manager
• xqemu manager could be a frontend that lists and downloads (or compiles!) specific revisions. That might be a better solution for the user.

[GXTX]

There was some talk in xqemu/xqemu#18 about including xqemu-manager with the AppVeyor artifacts. One of the ideas brought up was auto-updating (of xqemu-manager and/or xqemu). I don't believe auto-update should be included, or at the very least not defaulted on.

I've been personally burned by programs having auto-update enabled and having update servers get hacked (most notably puush). I understand the data would be coming from the official AppVeyor account for the XQEMU project but things can still happen that are undesirable.