Stratocumulus

* Add `--profile` option for all commands:
* Works for `aws` backend only. Allow use AWS profile other than default. If not using this option, use the default profile.
* Add `--quiet` option for `cp`, `sync`, and `rm` commands:
* If specified, Stratocumulus will not print the underlying AWS/GCP/Local commands on screen.

In `cp` command:
* Copying multiple files using wildcards now works for AWS backend.

In `exists` command:
* Make existence checking work for cloud folders in both GCP and AWS backend.

New command:
* `strato -v` or `strato --version` to check the version of Stratocumulus.

Make behavior of `strato sync` command consistent across backends.

* New feature:
* Add `--ionice` option for `cp` and `sync` commands, so that these operations can be run without monopolizing all the I/O bandwidth of local machines.