[entropy.client.interfaces.dep] move auto-conflict support to its own method

entropy.client.interfaces.package must use it during the install process as well
[entropy.client.interfaces.package] add auto-conflict support

The generation of the list of conflicting packages must also take
auto-conflicts into consideration, as the dependency calculation
code does. (This solves systemd vs openrc-settingsd when the former
doesn't say anything about the latter).
[entropy.client.dep] fix library based reverse deps calculation

Before adding a reverse dependency to the list, through library
metadata in _generate_reverse_dependency_tree(), take into consideration
all the available library providers.
Release Entropy 190
Tagging Entropy version 190