Branch-2802 Snapshot (Unreleased) HDFS-4076. Support snapshot of single files. (szetszwo) HDFS-4082. Add editlog opcodes for snapshot create and delete operations. (suresh via szetszwo) HDFS-4086. Add editlog opcodes to allow and disallow snapshots on a directory. (Brandon Li via suresh) HDFS-4083. Protocol changes for snapshots. (suresh) HDFS-4077. Add support for Snapshottable Directory. (Nicholas via suresh) HDFS-4087. Protocol changes for listSnapshots functionality. (Brandon Li via suresh) HDFS-4079. Add SnapshotManager which maintains a list for all the snapshottable directories and supports snapshot methods such as setting a directory to snapshottable and creating a snapshot. (szetszwo) HDFS-4078. Handle replication in snapshots. (szetszwo) HDFS-4084. Provide CLI support to allow and disallow snapshot on a directory. (Brondon Li via suresh) HDFS-4091. Add snapshot quota to limit the number of snapshots allowed. (szetszwo) HDFS-4097. Provide CLI support for createSnapshot. (Brandon Li via suresh)