Fixed location

[Christian-B]

The ChipAndCoreConstraint was the only constraint left

Yet there was a lot of overhead for a something rarely used.

These Prs remove all the constraint stuff and replace it with a fixed_location

The biggest change is that a vertex is no longer a ConstrainedObject so does have have a constraints param in its init.

Instead AbstractVertex (and therefor all vertex classes) have the methods
set_fixed_location(x,y,p=None)
and the
get_fixed_location which returns a ChipAndCore class IF and only if there is a fixed location BEFORE doing placements.

To avoid having to pass the fixed_location from ApplicationVertex to MachineVertex the get in the MachineVertex will fall back to the App if needed and possible.

The number of files changed show how much work was done for something used so little.

Must be done at the same time as:
SpiNNakerManchester/SpiNNFrontEndCommon#976
SpiNNakerManchester/sPyNNaker#1219
SpiNNakerManchester/MarkovChainMonteCarlo#34
SpiNNakerManchester/SpiNNGym#50
SpiNNakerManchester/SpiNNakerGraphFrontEnd#224
SpiNNakerManchester/SpiNNaker_PDP2#63

tested by:
SpiNNakerManchester/IntegrationTests#139

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