Corrected issue in relation to removal of models from canvases during a
branch. When a model is removed from a canvas, the removed model should
have its locator cleared to indicate the model no longer exists
"physically". If the removed model is not moved into another canvas
within the same branch, it is effectively removed and does no longer
exist "physically" in a persistent manner. This is interpreted as the
history of the model also no longer exists and the model should not be
registered, persistently, as an affected model.

Renamed method getLocation to getLocator in model.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>