This checks the checksum of the streamed encrypted data against the
checksum of the encrypted object returned from the remote and returns
an error if it is different.
* Implement about for:
* local, crypt, cache, drive, swift, hubic, onedrive, pcloud, dropbox
* Implement `--json` and `---full` flag for `rclone about`
* change About interface to return a Usage structure
* Remove operations.About as it is too thin an interface
* Implement Integration test
Relates to #1138 and #1564
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.