CT static API personality

[phbnf]

Previously: transparency-dev/trillian-tessera#88

Implements https://c2sp.org/static-ct-api

Pieces of work:

• port certificate-transparency-go CTFE to this repo, removing all the things we don't need anymore, and connect it to GCP Tessera to write tiles (no checkpoint at this stage)
  • break ground with an initial port
  • move more things over to drop dependency on non X509/TLS stuff from github.com/google/certificate-transparency-go (for instance github.com/google/certificate-transparency-go/trillian/util, github.com/google/certificate-transparency-go/trillian/testdata)
  • double check that tiles and leaf are compliant with https://c2sp.org/static-ct-api
    • Fix Data Type
    • Store fingerprints chain in leaves
  • have a look through all the old TODOs I ported over
  • move over handlers_test.go
  • add README and/or docker config to generate proto and mocks
• add a signer option
• design+build a chain storage service (see what we can re-use from Roger's recent work on certificate-transparengy-go CTFE): see #132
• design+build deduplication: ongoing
• design+modify configuration pipeline if need be: we've decided to stick to flags
• quota system: we've decided not rely on Tessera's pushbacks to start with. We'll add a quota system later if needed. See #186
• decide how we handle errors, and which one we pass to clients
• migrate codebase to a different repo
• load test with real world CT data
• deployment instructions Deployment instructions #21