Implement method of storing a "default" layout of nodes (as moved/saved by editors)

[kltm]

Related to #16, we need to have a method of saving the manual layout of nodes that does not rely on the participation of Barista.

After talking to Heiko a little and trying different thought experiments, we decided that the best method would be to essentially have a user option in a menu to save/snapshot the current layout ("Are you really sure you want to do this?"). The layout is bulk sent back to Minerva, where is is saved as your standard instance property. During initial layout:

algorithm < model instance hint < barista current location

[kltm]

Out of a discussion of #16, while this could be done in a "clever" way of having Barista inject this information during certain operations, there would be trouble with complete and up-to-date information. This is best done by a special op on the client that first scans the current locations.

[kltm]

Essentially a dupe of #113.