Auto update image from graph changes

[Potherca]

Although there is a sound logic behind having to submit a graph before the image is updated, it can be handy at time (working on smaller or more experimental graphs) to have an auto-submit/auto-update feature. This should be optional/settable through the interface.

[Potherca]

To avoid loading error/broken graphs, it might be wise to create a syntax check and only trigger an update when a graph can be created.

This could either be done server or client side.