remove: config.group_package_types.

Document this change.
remove: config.upgrade_requirements_on_install.

not used by the solver anyway.
rename: Base.activate_sack() -> Base.fill_sack().

More intuitive, sounds less technical.
rename: Base.build_transaction() -> Base.resolve()

More intuitive.
refactor: Comps.*iter methods are not properties.

Methods with iterators for return values are poor candidates for properties,
iterators are by nature quite mutable.
doc: delete the obsoleted API docs
Officially call dnf.yum.config.YumConfig just dnf.conf.Conf.
doc: disable html_static_path.

One less build-time warning.
doc: foundations of the API documentation.
INSTALLONLYPKGS cleanup, add installonlypkg(kernel)

Remove all unneeded and obsoleted installonly provides.
Add a new provide installonlypkg(kernel) intended to replace
kernel & kernel-source & kernel-devel in the future.
doc: api: Conf.installonly_limit.
New version: 0.4.7
build: 0.4.7-1
remove: repo._handle_new_pkg_download()

There was just one user left: repo.get_package(). DNF does not use it,
but we keep it for API compatibility. Refactored it to use the shared
destdir-free handle instead.