Fixed string comparison in DashboardTableNode.setStatus to use String.equals instead of == operator.
Issue: MIRTH-3227
Don't try to persist maps if the map content is null. Since we added source map in 3.0.2, this could occur if importing a message from 3.0.0 or 3.0.2. 
Issue: MIRTH-3111
MIRTH-3166, MIRTH-3201: For enabling/disabling/deleting channels, a single call to get the channels is now done first so that the cache only needs to be refreshed once. Also for deleting, the Channel object is passed in, instead of passing in the channel ID. This is so that it doesn't need to refresh the cache every time, and because the channel plugins need the entire Channel object anyway.