Monitor Process data storage inconsistent with earlier Lava probes

[mathisrichter]

The Monitor Process stores probed data such that the first dimension is the probed data itself and the second dimension is the current time step - the data arrays have shape (num_neurons, num_time_steps). The previous implementation of Lava probes used the convention (num_time_steps, num_neurons). This should be kept to enable using legacy code (e.g., for plotting) without modification.

[elvinhajizada]

@mathisrichter , thanks for pointing it out, I will issue a small pull request for this and maybe some other small Monitor related issues