Use a single persistent Experiment object for the whole GUI

[vnegnev]

Right now, each class defined in the seq folder creates its own Experiment object internally, and uses this to send over data. This isn't good because
a) it has processing and communication overhead, and
b) the Experiment class has some internal state (such as whether the gradient DACs have been initialised or not) which can't be used if you're making new objects each time.
I'd recommend refactoring the code to have a central Experiment object, and each seq class would just call its add_flodict() and run() methods. You then wouldn't need to keep calling __del__() each time it runs either - this also slows things down a little bit.

I can advise further if there are any questions.