Allows configuring the MultiplayerSynchornizer in a way similar to
AnimationPlayer.
Properties are added manually, edither as plain properties, or via the
NodePath format for child nodes' properties "path/to/node:property"
relative to the MultiplayerSynchronizer root path.
Nice things to add would be:
- Moving properties up/down in the list.
- Some form of keying, autmatic filling of the replication properity
line edit.
