Version flexible Virtual Machine

[Christian-B]

Part of the Spin 2 preparations.

Make getting Virtual Machines more Flexible

• Get a machine with a minimum of user cores
• Get a machine with a minimum chips
• Get a machine with a minimum boards
• Get a machine with a minimum size

To do this:

• The count of monitor (not scamp) cores moved to the Machine level
• Added Version methods size_from_n_cores, size_from_n_chips and size_from_n_boards

The virtual_machine_generator also uses the values saved in the DataView

Removed as many hard coded version dependant values from tests as possible.

Includes:
SpiNNakerManchester/PACMAN#557
SpiNNakerManchester/SpiNNFrontEndCommon#1175
SpiNNakerManchester/sPyNNaker#1441
SpiNNakerManchester/SpiNNakerGraphFrontEnd#273

Tested by:
SpiNNakerManchester/IntegrationTests#266

[coveralls]

coverage: 92.974% (+0.05%) from 92.928%
when pulling cdec110 on n_cores
into 00dfae5 on master.

[Christian-B]

fixes #240