- most of the things in utils/ are in the CalamaresUtils namespace,
let Permissions follow suit. Chase the name change in the
*preservefiles* module.
- add an `apply()` function for doing the most basic of chmod.
Note that we don't use `QFile::setPermissions()` because the
**values** used are different (0755 for chmod is 0x755 in the
enum value passed to `setPermissions()`).
- Expand the documentation, emphasize octal-vs-decimal
- east-const consistently in this file (most of Calamares is west-const)
- shuffle the is-valid bool to the end of the data members,
so sorting by size.
