Add REX support to cleos

[zorba80]

Change Description

Added cleos support for REX-related actions by creating cleos system rex subcommand and then sub-subcommands that correspond to different actions, for example:

cleos system rex buyrex user1account "1.0000 EOS"

The rex subcommands mirror individual REX actions. With one exception being lendrex that pushes two actions deposit and buyrex. The list of subcommands is:

Subcommands:
  deposit                     Deposit into owner's REX fund by transfering from owner's liquid token balance
  withdraw                    Withdraw from owner's REX fund by transfering to owner's liquid token balance
  buyrex                      Buy REX using tokens in owner's REX fund
  lendrex                     Deposit tokens to REX fund and use the tokens to buy REX
  unstaketorex                Buy REX using staked tokens
  sellrex                     Sell REX tokens
  cancelrexorder              Cancel queued REX sell order if one exists
  mvtosavings                 Move REX tokens to savings bucket
  mvfromsavings               Move REX tokens out of savings bucket
  rentcpu                     Rent CPU bandwidth for 30 days
  rentnet                     Rent Network bandwidth for 30 days
  fundcpuloan                 Deposit into a CPU loan fund
  fundnetloan                 Deposit into a Network loan fund
  defundcpuloan               Withdraw from a CPU loan fund
  defundnetloan               Withdraw from a Network loan fund
  consolidate                 Consolidate REX maturity buckets into one that matures in 4 days
  updaterex                   Update REX owner vote stake and vote weight
  rexexec                     Perform REX maintenance by processing expired loans and unfilled sell orders
  closerex                    Delete unused REX-related user table entries

Consensus Changes

API Changes

Documentation Additions