Add a table in db to hold runtime state info.

[yarkinwho]

Resolve #116

The table names or some may change.

And we may want to move some of the code to separate files

[taokayan]

Do we need to make the data field extensiable to hold some other information (such as gas configs) in the future? or at least make a version number into part of the data?

[yarkinwho]

Do we need to make the data field extensiable to hold some other information (such as gas configs) in the future? or at least make a version number into part of the data?

mdbx tables are pretty much kv stores, we can store anything in value. So if we want any more complicated mechanism for the value, we can always add later for the corresponding keys.

For the lib we want to use here, we do not need anything more than a number. So it's fine for now.