Protocol: add a flag on ChangeBoundsAction to distinguish resize vs move

[CamilleLetavernier]

While resize and move can generally be regrouped in a single "Change Bounds" action, it is sometimes useful to distinguish them, at least in two cases:

• Sometimes the bounds aren't 100% consistent between the client and the server. If the client sends its own version of the bounds during a Move, the server may interpret the action as a resize instead; so a Move could result in resizing the Node
• Some nodes may require some special behavior when moving vs resizing (When they don't use a simple X/Y Layout), so it may be useful to distinguish

The client (ResizeTool/MoveTool) should add a flag in the ChangeBoundsAction to indicate the kind of ChangeBoundsAction that should be triggered. On the default server side, there is probably nothing special to do; I don't think such a distinction is necessary for the generic cases.