add query tool
tests: repoquery: fix unit tests.
add pylint script for dnf-core-plugins.
rename: query->repoquery. (RhBug:1045078)
repoquery: some cleanups in the plugin and the tests.

E.g. lots of methods can be static or even outside of the command class.
repoquery: make the CLI more compatible with Yum's repoquery.
repoquery: support --provides, --requires etc.

Adds unit test for the cmdline parser.
doc: add reference documentation for repoquery.