Change config key names

* default_repo_target to repo_target
* gpg_key to gpg_keyid
Reorder statements in app.init()
Add conf.args.target checking to app.init()
Remove Repo() class and add test

More tests need to be written. This module is not complete.
Add backup_path to configuration options

When old packages are removed, they will be moved to the backup_path instead of
being deleted.
Move test_package_list() to test_package.py
Add copy_test_project_to_temp()

Copies a test project to /tmp for testing. Part of the file name is random to
prevent naming collisions.