Improve animation performance

[vicng]

Animation performance can be improved by making less calls to WorkspaceView.refreshView(), particularly when splicing in a new set of blocks into an existing block group. The reason is that it's expensive to make multiple changes to UIScrollView properties inside an on-going animation (which is what WorkspaceView does).

This can be done once WorkspaceLayout is refactored, where there is more granular control over how layout updates are performed on block disconnect/connect.