AGPUSH-848 : Number of devices shown in Dashboard do not match number of installations

After having discussed this on the ML ( http://lists.jboss.org/pipermail/aerogear-dev/2014-August/008599.html ) , here is a PR that now shows the last 3 "active" Push activities. It's not the ultimate solution but it could be improved later and at least it now shows accurate information.