Update account.PublicKey to account.BJJ for naming consistency with the rest of the code

Update usage of `*babyjub.PublicKey` to `babyjub.PublicKeyComp`
- when the key is not defined, internally is used `babyjub.EmptyBJJComp`, which is a `[32]byte` of zeroes of type `babyjub.PublicKeyComp`
- the API continues returning `nil` when the key is not defined

Checked with commonjs version:
c8414bd205

Change endianness to BigEndian (ಥ﹏ಥ), spec has been updated to achieve
compatibility with js & smart contracts & circuits implementations.

Update log package with fields & file log, and update constants in the
repository code to be MixedCase.

resolves #91, resolves #92, resolves #95

- Update GHA lint.yml increasing timeout time to avoid GHA Lint errors
- Update common.BatchNum & common.Idx & common.Nonce usage in StateDB
- Add abstraction method of processTxs to StateDB
    - Which will be used by Synchronizer & BatchBuilder