T2730
Stacked diff to localize existing uses of BCH.Mnemonic throughout the app and deprecate the BCH.Mnemonic object.
Relies on the BIP39 library for mnemonic operation.
**Pt 1/6 - Implement BCH.Mnemonic.toSeed locally**
Pt 2/6 - Implement BCH.Mnemonic.generate locally
Pt 3/6 - Implement BCH.Mnemonic.wordLists locally
Pt 4/6 - Implement BCH.Mnemonic.validate locally
Pt 5/6 - Deprecate BCH.Mnemonic throughout the app
Pt 6/6 - Optimize bip39 bundle via webpack IgnorePlugin