Add version, checksum, and partial state indicator to intermediate migration payload file

[fxamacker]

We recently added feature for state extraction to produce a payload file (intermediate file during migration) along with a flag to specify desired addresses (accounts) of payloads to include.

This payload file is intended primarily to speedup development, testing, and debugging of migrations.

However, it is possible partial state may also be used accidentally for real migrations.

For these reasons, adds more metadata to the payload file:

• file format version
• partial state vs full state indicator (e.g. whether it includes payloads for all accounts or some)
• checksum

Also, to prevent accidental use of partial state, add a flag to state extraction tool that must be specified by user in order to use payload file not marked as containing full state (i.e. when file doesn't have payloads for all accounts).

Thanks @zhangchiqing for suggestion to add checksum to this payload file, etc.