Rosetta zendoo sidechain update

[paologalligit]

Rosetta needs to be updated to support all the new sidechain operations:

• sc creation
• forward transfer
• backward transfer
• sc certificates

The task could be divided into:

• update data types (data API) #8

• update new tx constraints (construction API) (e.g. backward transfer coins cannot be spent until the end of an epoch) #9

The update branch is sc_update