xmonad-log-applet 2.1.0 version bump and 2.0.0 stable keywords

I am not sure about the policy regarding stable keywords in the gentoo haskell overlay, but xmonad-log-applet 2.0.0 has been there a long time and though that it would be about time to mark it stable. If this is against any policy simply ignore the second commit :-)

The first one is simply a version bump to 2.1.0. A new feature of xmonad-log-applet was the support for the mate desktop environment, but since there are no ebuilds for mate this feature is not available in the ebuild.