Redline: Local staging area for drawn redlines

[jng]

The problem with the current redline widget is that each redline drawn triggers a map refresh. When redlining against a heavy map, this is somewhat undesirable behaviour.

To alleviate this problem, we should support a local staging area where drawn redlines go. These are OpenLayers.Feature.Vector objects sit in a OpenLayers.Layer.Vector until the user commits the whole set of features up to be saved to the Redline feature source

This is somewhat similar to the feature [create/checkout]-edit-checkin workflow for AutoCAD Map. The main benefit of this is improved efficiency as the user can draw multiple redlines in succession without an automatic refresh (unless the user pans/zooms around while drawing)