Add ability to record and replay lists of ASync copies

[chrisgearing]

By linking togeather a multiple ASync copies into a single user level transation the opportunity for gather scatter type operations becomes possible.

This patch only allows this in the row axis, which may be the only axis that makes sense due to the nature of the underlying storage.

An income tensor can be gathered in any order, for example.

A 10 row global Tensor could be mapped to a 4 row local tensor with the following mapping Global Row 1 -> Local Row 1 Global Row 6,7 -> Local Row 2,3 Global Row 3 -> Local Row 4

The mapping is passed to the tiler, and from that point forwards is invisible to the user.

[CLAassistant]

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