Implement file mtime,ctime,atime

[dannycjones]

Today, all files have an 'mtime' or last modified time of 1st January 1970.

We should use the creation date of the object (LastModified) for the 'mtime' (last modified time). We may also want to use this value for 'ctime' (inode change time) and 'atime' (access time) as well, but not sure on this.

[andywarfield]

Setting all three times to be creation time is consistent with S3 semantics. We should make sure to document that we are effectively doing default noatime here. We've talked about the idea of having different modes/personalities for the connector in the future, so it might be worth thinking about how to structure this in a way that helps support that later.