Accept 3 letter prefix for seed phrase words

[AleryBerry]

Fixes #566

Description

If it's restoring a monero wallet by mnemonic phrase, it only needs 3 letter prefixes for every word to validate.

Pull Request - Checklist

• [x] Initial Manual Tests Passed
• [x] Double check modified code and verify it with the feature/task requirements
• [x] Formate code
• [x] Look for code duplication
• [x] Clear naming for variables and methods