Allow open endpoints to be 'configurable'

[iAmMichaelConnor]

At the moment, all routes are open.

Some open routes pose could result in a user's DB being corrupted. No private info would be leaked (because Timber doesn't hold any private info). But apps which make use of Timber's DB might fail to be able to 'spend' commitments if a DB is corrupted. They'd then need to re-download the entire merkle tree again (by having Timber filter the blockchain again).

How could the DB be corrupted? E.g. a user could accidentally push leaves directly to the DB by calling the PUSH /leaves route.

New 'configuration' options (which allow users to close certain endpoints) should be added.

[iAmMichaelConnor]

@willKim19 tagging you for visibility :)