Reasoning why this is part of the core and not a separate addon:
The impact of this function is extremely lightweight when (almost) no
aliases are defined so someone who isn't using this should not have a
worse experience.
Additionally including it in the core (similarly to the discounts,
taxes and restrictions) promotes it's availability while not massively
increasing the maintainability.
As for the OddItem removal:
That plugin hasn't been developed for over 7 years and such unique
plugin support should really be added via separate addon using the
events system which, with the new ItemStringQueryEvent, now actually
supports doing that from an external plugin.
If someone really managed to run their own private fork of OddItem for
all those years then they should be able to also provide such a simple
addon.
The configuration isn't loaded yet when the plugin loaded and the flag initialised so we can't check that there. The config option is checked at the point where the flag is handled though so there is no difference from the intended functionality when registering the flag anyways. The only downside is that this could be a tiny bit confusing to the user in the end but I think that is a small price to pay when it wouldn't be working at all otherwise.
This introduces a new AccountCheckEvent to check if a user actually has an account with the used economy plugin. Also fix CurrencyTransferEvent logic (even though it's not used anywhere currently)