Add spec for order transaction ordering within blocks

[TomMcL]

Add a spec for ordering transactions within a block for a given market such that post-only changes and cancellations come first, allowing market makers to offer tighter prices with less risk from toxic flow.

#2231

[davidsiska-vega]

Make sure we're clear that batches either:

• contain nothing "potentially aggressive" (post only orders, or cancels) in which case the whole batch gets priority and doesn't get delayed. If it has amends it's potentially aggressive.
• if the batch contains a single aggressive transaction it gets delayed

1, Standalone cancels
2, Batches as a whole
3, Standalone creates

Make sure we mention that delayed orders need to go into snapshots.