T2730
Depends on D12450
Stacked diff to localize existing uses of BCH.Mnemonic throughout the app and deprecate the BCH.Mnemonic object.
Relies on the randombytes library.
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