Working config forwarding to browser.

Element configuration updates are now forwarded to browser via
SSE. Have to read up on how to best solve the issue of initial
syncro though. The most straight-forward way is to make the channel
replay everything but I don't yet know how to achieve this with
play.
Browser can now ask for node creation at a specific location.

Added /add endpoint taking a nodetype, x and y for node creation.
Return value is the id of the newly created object.

Added js functionality for accepting creation by click.

Improved templates so unneeded script and css isn't loaded on
all pages.
Browser can now react to element configuration updates.

Can now create objects on demand. Pretty limited at the moment.
Added notion of input/output arity as well as display.

- Added input/output count to FlowNodes.
- Added display for that in the browser.
- Added display fields which can be used to expose select
  fields of the node state to the user.
- Played a bit with the css
Complete basic behavior for node backend/frontend interaction.

- Supervisor now replies to disconnect requests
- New /connect endpoint for introducing connections
- New /disconnect endpoint for dissolving connections
- New /postNode/:id endpoint taking a json config update for a node
- /reset now runs a configuration detection
- Frontend can now establish and dissolve connections
- Frontend can now propagate item movement
- Updated to jsPlumb 1.6.3 dev (1.6.2-14-g779140e). jsPlumb 1.6.2 had
  a bug and didn't call beforeDetach handlers in all detachment situations.
  Issues was already upstream (https://github.com/sporritt/jsPlumb/issues/223)
  known upstream and promptly fixed.

Note: There's no way for clients to receive remote updates on connections yet.
      Also sync on connect hasn't been tackled yet.