libdeng2|File: Don't return a reference to private member
Cleanup
libdeng2|Log: Keep track of the current log entry metadata

This information can be used by methods composing text for log
entries.
libdeng2|FS: Attempting to improve readability of file descriptions

A file description now adapts to the current log entry metadata in
that more verbosity is included for developer/verbose entries.

PackageFolder now describes itself as a "package" rather than
"folder."

test_archive now tests the three possible levels of file description
(with a PackageFolder and a NativeFile).