This commit consolidates some of the smaller files into some of the larger files.
The smaller files cluttered the file tree and made it harder to see the logical
groupings of structs.
This commit changes the API for:
Tx.CreateBucket()
Tx.CreateBucketIfNotExists()
Bucket.CreateBucket()
Bucket.CreateBucketIfNotExists()
These functions now return the *Bucket and error instead of just the error.