Fixes #258 - leave it up to geoserver/FTL to determine which links are external and which are not.
Create global strings for message bus events

I think using variables for message bus names is a good idea if for nothing other than speeling.
Fixes #271 animation panel disabled if layer added before caching completes

Publishing a beforeSelectedLayerChanged event in the ActiveLayersPanel solves the issue.
Merge branch 'master' into issue-271
Merge pull request #300 from aodn/issue-271

Issue 271