Support Larger Files with Asset Data Type

[ezfe]

I put this PR together to show how this would work, and did a quick test to make sure it worked. This pull request changes the data type from Bytes to Asset, and creates a new CKAsset when uploading.

Note: This does not convert existing records, so I changed the field name from data to asset to keep compatibility.

[mxcl]

I am actually reluctant to change this before someone presents rationale for it.

The tool is not designed for large files, we don’t diff for example, so everything is uploaded/downloaded every time a change happens.

[ezfe]

Of course, that makes sense, I didn't put much work into this and I just wanted to see your thoughts. Feel free to close this PR at your own discretion.