[ISSUE #192]Optimize BossCommand code and add ServerCommand

[mxsm]

Fix #192

• Optimize BossCommand code and add ServerCommand
• GetCommand，LeadershipTransferCommand，ReadFileCommand add Parameters annotation and add command description for each.（Tips: AppendCommand command description was added in this PR [ISSUE #187] DLedgerClient batch append entry Support #188 ）

Usage: <main class> [command] [command options]
  Commands:
    server      Bootstrap DLedger Server
      Usage: server [options]
        Options:
          --group, -g
            Group of this server
            Default: default
          --id, -i
            Self id of this server
            Default: n0
          --peer-push-quotas
            The quotas of the pusher
            Default: 20971520
          --peer-push-throttle-point
            When the follower is behind the leader more than this value, it 
            will trigger the throttle
            Default: 314572800
          --peers, -p
            Peer info of this server
            Default: n0-localhost:20911
          --preferred-leader-id
            Preferred LeaderId
          --read-only-data-store-dirs
            The dirs of this server to be read only
          --store-base-dir, -s
            The base store dir of this server
            Default: \tmp\dledgerstore

    readFile      Read data from DLedger server data file
      Usage: readFile [options]
        Options:
          --body, -b
            if read the body
            Default: false
          --dir, -d
            the data dir
          --index, -i
            the index
            Default: -1
          --pos, -p
            the start pos
            Default: 0
          --size, -s
            the file size
            Default: -1

    get      Get data from DLedger server
      Usage: get [options]
        Options:
          --group, -g
            Group of this server
            Default: default
          --index, -i
            get entry from index
            Default: 0
          --peers, -p
            Peer info of this server
            Default: n0-localhost:20911

    leadershipTransfer      Leadership transfer
      Usage: leadershipTransfer [options]
        Options:
          --group, -g
            Group of this server
            Default: default
          --leader, -l
            set the current leader manually
          --peers, -p
            Peer info of this server
            Default: n0-localhost:20911
          --term
            current term
            Default: 0
          --transfereeId, -t
            Node try to be the new leader
            Default: n0

    append      null
      Usage: append [options]
        Options:
          --count, -c
            append several times
            Default: 1
          --data, -d
            the data to append
            Default: Hello
          --group, -g
            Group of this server
            Default: default
          --peers, -p
            Peer info of this server
            Default: n0-localhost:20911