shares: implement/import DASing

[Wondertan]

Context

Celestia light clients heavily rely on DASing and we need to implement it in the Node.

Implementation

Luckily, most of it has already been implemented in core. The first step would be copying the code from the Core in the specific branch. It may be needed to copy more code than just the ValidateAvailability function. Then, we should aim to extract all the DASing(share) related code into a separate repository(#21).

[liamsi]

My understanding is that this is done now?

[Wondertan]

Yes, thank you!
Closed by #177