Integrate the new keystore in PXE

[benesjan]

Nuke the original key_store.ts and replace it with the new ones.

A few large changes will need to get done in this PR:

1. Make PXE handle multiple key stores instead of just one --> originally we had 1 key store per PXE and the keystore could contain multiple accounts. I feel like having one account per keystore is nicer because that's how it's done in geth and it feels more natural.
2. We will need to update oracles and APIs.