Suggestion: Handle failures in individual update checks more gracefully

[NoiTheCat]

If one of the items that updates are checked against fails, the applet does not show anything regarding other updates. For example, as most recently implied in #146, a failed attempt to fetch widget information caused the applet to not return any updates for pacman and AUR.

My suggestion is allowing individual checks to fail without stopping the rest of the process, and then reporting the failures however possible.