Encode the tx inputs/outputs order in *TxLayout type for each tx type

[greenhat]

Motivation

In some contracts, often, there are required box positions for particular boxes (refresh, pool, buyback boxes, etc.). Usually, the order is defined by adding boxes to the vector, which is error-prone (think swapping two lines of code).

Implementation details

*TxLayout is constructed with specific *BoxWrapper types and produces the box array for a tx builder.