Implement the feature to convert ICon.Contract

[taiseiKMC]

Try to implement the contract part of https://github.com/westpaddy/icon-why3/blob/nishida/contract-ty/req/gparam.md

• the entrypoint type definition follows the implementation by Jun
• the contract type definition follows that specification above
  • s.t. type contract = { ct_ep : entrypoint; ct_addr : address }
• Xfer receives 3 parameters: gparam, mutez, and contract
  • Reverted 4 to 3. entrypoint and address are merged into contract (because it seems to have no problem)
• ICon.Contract addr is converted to { ct_ep=(Default : ICon.Contract.entrypoint); ct_addr=addr }
• ICon.Contract.ep addr is converted to { ct_ep=(Ep : ICon.Contract.entrypoint); ct_addr=addr) }

and some fixes (I commented in #30) and dao.tzw example that includes an entrypoint receiving a contact parameter.

[taiseiKMC]

Though the feature to convert ICon.Gp also has the same problem, local opened ICon can not be handled

ICon.(match st.entrypoint, gp with
| Contract.Default, Gp (p : ()) -> True 
    (* Contract.Default is acceptable, but Gp isn't *)
| _ -> True
    end)