Allow SubviewCollectionGroup to be configurable on initialisation; Change the plumbing components to play along.
Moved DiagramViewEndpoints to endpoints submodule, renamed it to DiagramEndpointGroup
Moved DiagramViewConnections to connections submodule, renamed it to DiagramConnectionGroup
Removed the now redundant DiagramViewConnections
Create and use DiagramStateGroup and StateEndpointGroup for future specialising
Cleanup for the plumbing views' overrideable properties
Allow plumbing components' group types to be overrideable
Merge branch 'develop-frontend' into feature/issue-399-plumbing-components-need-refactoring
Merge branch 'develop-frontend' of github.com:praekelt/vumi-go into develop-frontend