backbuffers activated for default.wmc baselayer, see #41
release notes updated
merge with master
Merge branch 'master' into feature/41/backbuffers
apply transitionEffect resize to opaque WMS layers
update openlayers submodule in order to be able to write layer.transitionEffect into WMC
Merge pull request #42 from georchestra/feature/41/backbuffers

Ability to activate backbuffers on layers coming from a WMC