rename: callback.Progress -> callback.DownloadProgress.

There might be other progressing things too besides network downloads.
api: document dnf.callback.DownloadProgress and friends.
refactor: Payload makes more sense to live in dnf.callback.
New version: 0.4.15
build: 0.4.15-1
refactor: Move InfoCommand._print_packages to BaseCli.output_packages.
refactor: Move repo-pkgs info to a standalone class instead of reusing the InfoCommand.
refactor: Move MockBase methods to BaseStubMixin.
Fix "repo-pkgs info installed" behavior with respect to the documentation.
tests: Add tests of repo-pkgs info against the documentation.
refactor: Move repo-pkgs list to a standalone class instead of reusing the ListCommand.
refactor: Move repo-pkgs check-update to a standalone class instead of reusing the CheckUpdateCommand.
refactor: Move CheckUpdateCommand.check_updates to BaseCli.
Drop "repo-pkgs install @Group" support.
Drop group filtering by repository name from installPkgs.

This partially reverts commit 4e236b36744866add4310a198a59a78a19b66200.
Revert "Support filtering by repository name in Base.select_group."

This reverts commit d125a43dc726174f1fff0902abb50aeac4ecaf78.
Revert "Support filtering by repository name in install_groupie."

This reverts commit 02d2e38c01c1df1e4976f400d24798f2d036d907.
refactor: Move repo-pkgs install to a standalone class instead of reusing the InstallCommand.
refactor: Remove the reference to installPkgs from InstallCommand.
refactor: Remove the reference to installPkgs from InstallSubCommand.