including .mo files correctly
comps: _by_pattern() no longer does the comma splitting.

In no universe was that a wise thing on this level.
fixed not including .mo files
fixes TypeError: '_DownloadErrors' object is not iterable (RhBug:1078832)
AUTHORS: added Tim.
test: fixed CacheTest.test_noroot() when running as root
AUTHORS: added Albert.
rename: make cli.commands a subpackage.

So we can start splitting out the specific commands.
refactor: put GroupCommand into its separate module.
packaging: add dnf.cli.commands to the installation.
downloads: bump number of downloaded files on a skip. (RhBug:1079621)
New version: 0.4.19
build: 0.4.19-1
kernel: remove kernel-source from const.INSTALLONLYPKGS.

Related: RhBug:1062997
Related: RhBug:1079906
refactor: groups: make all commands use _patterns2groups().
refactor: imports order in cli/commands/__init__.py.

Drop a couple too.
doc: cli_vs_yum: we do not partially allow operations that install .srpm. (RhBug:1080489)
doc: cli_vs_yum: typography in bandwidth limiting section.
rename: persistor.Groups -> ClonableDict.
groups: besides installed groups also store persistently the environments.