Got new gpu code to a point where the sim runs.

Doesn't run correctly, but its a start!
Got probing of decoded values working.

For the new gpu lib.
GPU assoc lib now uses radius.
Bunch of small fixes.
Moving towards non-identical case.
Better seeding.
Changed order of operations.

To better reflect the order used in Nengo 2.0. In particular, to
reflect the fact that writing to the output of a neuron is an update.
Now using nengo's hierarchical seeding.

Currently only available on hierarchical_seeding branch.