Add class for representing package
Represent packages as objects instead of dictionaries
Do multiple changes - use argument parser, package class and implement `--now`
Sorry for this commit, but I have to do it this way.
Changes:
- Use argument parser from previous commit
- Use package class from previous commit instead of dictionaries
- Implement `--now` functionality. When its used with specified packages, `NOW` is set as modified time, so there is no openning DNF database