Fix "Duplicated Account" problem caused by KeyringContainer.remove()

[aeharvlee]

Proposed changes

This PR fix "Duplicated Account" problem caused by KeyringContainer.remove().

Because Keyring Container.add() and Keyring Container.get Keyring() both use lower cased address,
Keyring Container.remove() should guarantee its input address is lower cased.

You can re-produce error by following below sequence.

1. Add your keyring to wallet using caver.wallet.add() with address having lower and capital letter both. (e.g. 0xca04A7e79072CE7edd3C1B0bFAdDe496806a16AD)
2. Update your keyring using caver.wallet.updateKeyring() with new keyring which have same address in sequence 1 and different private key.
3. Then you can see the error "Duplicated Account. Please use updateKeyring() instead".

Here is the Gist RemoveErrorTest.java for more detail. You can test yourself with this Gist and KAS

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