Replacing the term `App` with `Account`

[YaronWittenstein]

Originally, the App term has been introduced in order to distinguish between two different kinds of Account:

• Simple Account
• Smart-Contract Account

Recently, the team has voted for shifting towards the Account Abstraction (a.k.a Account Unification) model.
This decision turns the App term to being redundant.

Moreover, keeping using the term App it might cause confusion to people since there is no difference between an App and Account - all Accounts are now (for the v0.3) of the same model.

This means that we'll use this terminology:

• Deploy Template
• Spawn Account (out of a given Template)
• Call Account

Related:

• Account Unification SMIPS#49
• C-API changes #253

[lrettig]

Makes sense, but I still think we may need a term to refer specifically to the code portion of an account, and we may also need to differentiate between classes (e.g., templates) and instances. Saying "execute an account" sounds a bit strange to me. As one point of comparison, Diem/Move has two types of "programs": "modules" and "scripts" (https://developers.diem.com/main/docs/move-modules-and-scripts). I like this terminology.

[YaronWittenstein]

An Account encapsulates a couple of properties. One of them is the code.
Why not just call it The Account's code?

Also, an Account is an instance of a Template