Unexport HashLogRoot. Verify with VerifySignedLogRoot. (google#1042)

* SignedLogRoot <-> VerifySignedLogRoot

SignLogRoot should produce a *trillian.SignedLogRoot
VerifyLogRoot should verify a *trillian.SignedLogRoot

This prevents clients from needing to parse the SignedLogRoot object
themslves. It also provides a single API point to maintain.

VerifySignedLogRoot will produce a *trillian.SignedLogRoot.
The idea is the force clients to only use data that has been returned
from a successful verification.

* Unexport HashLogRoot

* reviewer edits

Many internal API changes for storage. Start of mirroring. Some schem…

…a changes

GetLeavesByRange, frozen, signer metrics

TLS, Merge delay metrics, admin testing easier

Master signing, vendor updates to etcd and grpc

Auth API, interceptor fixes, docket updates, sqllite some other stuff.

Tree GC, go 1.9, update private keys

Batched queue

First production ready version

Hasher registry. pkcs#11 support. CONIKS