[refactor]: Shallow objects in `data_model`

[Erigara]

Currently objects in data_model are nested. Domains contain Accounts and AssetDefinitions inside it, Accounts contains Assets and Roles and so on.

We should consider making objects shallow: so that all Assets would be sotred in the single place and only reference owner Account by it's AccountId.

This way iteration over objects will be more effective.

As a sidenote such structure more closely resemble data organization typically encountered in relational databases.

[mversic]

let's consider after new wsv

[Erigara]

Another benefit comes from how our new state works, which favors granular updates to avoid extensive cloning.

[SamHSmith]

First PR was merged.

[nxsaken]

Apparently, we're moving to a sort of static Entity-Component-System / Struct of Arrays, so all data model structs should eventually disappear.

[SamHSmith]

This issue is about how the code should be structured. PR's containing these changes have been merged already. Therefore the issue is closed.