Two-way Server-side slide notes fix

Modified the notes-server plugin to support control from the remote
notes viewer.  Use the pop-up or the link in the javascript console to
view slide notes remotely.

Also added support for ./presentations off the root path to contain
additional presentations.  This way you can clone the repo and either
create+ignore that path or submodule your own repo into its place.
This fix only works for  the notes-server plugin (node
plugin/notes-server).