improvements to updater flow

[anmolbyte]

First off, thank you for making this app- it's been incredibly useful.
However, it seems to check for updates when librewolf is open and only downloads and installs when librewolf is closed. This doesn't make it as seamless as the chromium autoupdater task, which automatically updates chromium without any popups or need for the user to close out of the browser. To this end, I am suggesting a different flow method:

1. Check for updates independent of the browser (i.e check at login for a new version of librewolf)
2. Automatically download the installation package even if librewolf is open
3. Install the next time that librewolf is launched, or before that if librewolf is closed

I think the first 2 steps can be done, but I am not sure if step 3 can be done if you don't have access to the install directory. I believe that you would have to "hijack" the application launch shortcut. But making so that the program downloads the librewolf installer in the background while the browser is still open would reduce browser downtime.

[ltguillaume]

1. It seems like you're using the portable version if (1) is an issue, because WinUpdater already provides automatic checks via an optional scheduled task outside of the portable version. Portable versions should never install anything like that on a system.
2. This would be possible, but I chose to check for a new version again after LW is closed. This is because there might have been a new release between the first check and the time LW is closed. I could change this into download > check for new version on close > redownload if necessary, that would indeed save some time.
3. Why? It already updates as soon as LW is closed.

I think (2) makes sense, but the actual updating works differently for Chromium-based browsers, as they're installed in a separate folder of their version number, while LibreWolf files have to be overwritten.