Rename Contract.wallet to Contract.account

[marcelomorgado]

Or maybe setSenderAddress and getSenderAddress in case we want to set it to a contract-based account?

Getter/Setter should be renamed too.
Refs: #357 (comment)

[marcelomorgado]

Good question. We can have these situations:

• Same account as the signer and sender;
• An account as sender and one as the signer;
• An account as sender and many as the signers;

[pcowgill]

Good question. We can have these situations:

* Same account as the signer and sender;

* An account as sender and one as the signer;

* An account as sender and many as the signers;

Yep. Supporting and testing all of those situations is important (and maybe outside the scope of this issue based on its current name?)

[marcelomorgado]

For short-term we can just rename from wallet to `account and then split this issue to continue the discussion of how should be the Contract API to support the situations above. Make sense?

[pcowgill]

For short-term we can just rename from wallet to `account and then split this issue to continue the discussion of how should be the Contract API to support the situations above. Make sense?

Yep, perfect!

[marcelomorgado]

Discussion about API extracted to: #375