Fix `rand()` and `rand()` in Python code, which created random number arrays of the wrong size for size-one index arrays.
Document the new time/dt/scheduling system (as if it were already implemented)
First steps towards the new scheduling system
Most problems fixed (except: recording from subgroups, changing dt for spikequeue)
Fix monitors (no need to use the source's clock, monitors can use their own clock)
Fix an overwritten `dt` attribute in `SynapticPathway.initialise_queue`
Use the floating point value of dt, not the `Quantity` as the key for the dictionary in `_determine_clocks` -- otherwise it won't work in Python3
Update some more tests to work with the new clock system.
Make sure that the order of objects in a `Network` is deterministic, even for arbitrary orderings (same dt, when and order attributes).
Don't hide failed `get_value()` calls in `AttributeValue` when transforming the variables dictionary into the final namespace.
Adapt the test that refers to `t` with a 0ms run to make sure that a clock exists.