Allow MML files to be provided

[BHare1985]

Use millistone to be able to take in a .mml file.

I don't think modifying grainstore is worth while, instead make a wrapper including grainstore that encompasses all 3 inputs (grainstore/mml (millstone)/xml)

• Take in local mml file with local datasource
• Take in local mml file with remote datasource
• Take in local mml file with remote zipped datasource
• Take in remote mml file and treat it like a local mml file