Add passphrase letter case validation

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Expected behaviour

Entering a passphrase with any uppercase letter should inform the user that it is not valid passphrase.

Actual behaviour

Entering a passphrase with any uppercase letter results in being logged into a different account.

Steps to reproduce

• Login with dolphin inhale planet talk insect release maze engine guilt loan attend lawn
• The address will be 4264113712245538326L
• Logout
• Login with Dolphin inhale planet talk insect release maze engine guilt loan attend lawn
• The address will be 17940473436127707595L