Add repository file actions and upon import copy files to correct location

File actions for repository files (e.g. copy, symlink, move, remove) implemented with repod.repo.package.repofile. CLI subcommand repod-file package import replaced by repod-file repo importpkg, which also implements the copying of files to a given repository's package pool and handling of symlinks in the package repository directory.

The deliverability check for the email in the Packager model is disabled by default now until it will be made configurable with #92 (to not require network access during testing).

A problem with the usersettings test fixture has been fixed. It no longer leaks test state into the user system.

Fixes #14 (closed)

Closes !40 (closed)