T2730
Depends on D12452
Stacked diff to localize existing uses of BCH.Mnemonic throughout the app and deprecate the BCH.Mnemonic object.
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