when initiating a call;
- from header
- account
These 2 parameters are dependent from each other which makes tricky for
the core to know exactly which account to use and the correct from
address.
In most scenarios, the from address is the account's identity address
but it is not always the case such as in the case of a direct call.
Moreover, the account cannot be always deduced in a straightforward
matter such as if the core has no default account (but it is registered
with one or more accounts) and the call parameters have not set one.

The algorithm for choosing an account is the following:
1) search in the call parameters
2) get the default account
3) look up for the best guessed account based on the from (if known) or
   to address

The algorithm for known the from address is the following:
1) look for the from header in the call parameters
2) look up for the identity address of the account (if known)
3) get the core primary account

...