Always pass account when specified

[AngryAnt]

Specifying an account for op is not only useful when required. In an app-integrated setup where you have multiple accounts configured (like the scenario of a company account and a private one), passing the account when provided is critical in resolving requests.

This change keeps existing behaviour of excluding the parameter from some commands and failing when an account is required, but not provided. Outside of that, the account parameter is now always provided if set.

Example of use in app-integrated context:

s_Manager = new OnePasswordManager (
	new OnePasswordManagerOptions
	{
		AppIntegrated = true,
		Path = kBinariesPath,
		Executable = "op"
	});

s_Manager.UseAccount (kAccountID);

[jscarle]

Looks good, thanks for the contribution!