bug: Allow to set chunkSize to be set in dataSquare

[walldiss]

If DataSquare initialised without chunks, SetCell will return chunk size mismatch error on setting first chunk with non 0 size. We need a way to create square without chunks, that will allow SetCell and will be possible to use GetCell on. Currently, there is no way to initialise square, providing no chunks and setting chunkSize to non zero value at the same time.

Steps to reproduce:

1. Create new DataSquare by newDataSquare with data list of 0 length.
2. Set shares by SetCell

Solution:
Add chunkSize param to the newDataSquare constructor

[Wondertan]

Additionally, we can follow implicit approach of the constructor and set chunk size on the first SetCell call

[Wondertan]

@walldiss could you provide an example of the code that is required to make it work correctly? Can be copied/directed from our hotfix

[rootulp]

Solution:
Add chunkSize param to the newDataSquare constructor

Since newDataSquare isn't exported, celestia-node invokes ImportExtendedDataSquare. The chunkSize param needs to be added to both newDataSquare and ImportExtendedDataSquare. Additionally, celestia-node is calling ImportExtendedDataSquare on an empty data square which seems odd. Related #85