Move Message Types to Their Respective Crates

[mccallofthewild]

As raised in #24 (comment), the consolidation of message types into a single crate makes contracts less readable. Futhermore, it may cause cargo to behave inefficiently, recompiling all reverse dependencies every time a the ultra-base crate changes.

Definition of Done

• All message types moved from ultra-base to their respective contracts/<contract>/msg.rs

[mccallofthewild]

Considering closing this, as many contracts are interdependent and we cannot write them all at once, so having all message types in one place enables us to develop using message types that don't have implementations yet.

[mccallofthewild]

WIP in: mccallofthewild/flatten-types