Support generate open transaction message to sign

[TheWaWaR]

Provide apis to read all data of an open transaction for sign, include all input command and according data to read.

The cell mask:

The full current transaction hash
length of input & output cells in current script group
data from input and output cell:

| 0x1   | Capacity         |
| 0x2   | lock.code_hash   |
| 0x4   | lock.hash_type   |
| 0x8   | lock.args        |
| 0x10  | type.code_hash   |
| 0x20  | type.hash_type   |
| 0x40  | type.args        |
| 0x80  | Cell data        |
| 0x100 | Lock script hash |
| 0x200 | Type script hash |
| 0x400 | The whole cell   |

The cell input mask: data from CellInput structure:

| 0x1   | Capacity         |
| 0x2   | lock.code_hash   |
| 0x4   | lock.hash_type   |
| 0x8   | lock.args        |
| 0x10  | type.code_hash   |
| 0x20  | type.hash_type   |
| 0x40  | type.args        |
| 0x80  | Cell data        |
| 0x100 | Lock script hash |
| 0x200 | Type script hash |
| 0x400 | The whole cell   |

[TheWaWaR]

Draft implementation: https://github.com/liuck8080/ckb-sdk-rust/tree/opentx_sign_tx