[CO-325] Add 'MnemonicError' prefix to build instances of MnemonicError
[CO-325] Add 'MnemonicError' prefix to build instances of MnemonicError

This gives a bit more context to understand where the errors come from if they randomly pop-out in the wild

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype