Importing with 12 mnemonic words: a better interoperability between browser wallet and cli

[kayagokalp]

Problem

Currently the wallet browser extension supports importing seed phrase in 12 and 24 word configuration. But while exporting they only export 12 words. forc-wallet on the other hand supports importing only 24 word mnemonics and exports only 24 words as well.

This means we cannot import a wallet generated by the extension to forc-wallet cli.

Suggested Solution

Support 12 word mnemonic import as well (to be feature proof let's see if we can also support exporting with 12 words as well).