Add APIs for managing TLDs

This change adds APIs for managing TLDs. Previously TLDs were in
2 files. With this change, the TLDs will be in the central's storage
database.

When the service starts for the first time, by default there are no
TLDs in the database.  When there are no TLDs in the database
the behavior is to not check for TLDs when creating domains.
Once a TLD is created in the database, the TLD checks are
enforced.

Change-Id: Ibc945af3b158355475f5c8ee7887ed4b32081337
Merge "Add APIs for managing TLDs"