LibsolvSolver: Automatic whitespace cleanup
BSolverRepository: make polymorphic
BSolverRepository: Add {Remove,Delete}Package()
BSolver: Extend FindPackages() functionality

* Add flag B_FIND_INSTALLED_ONLY to only return installed packages.
* Add FindPackages() version that finds packages like Install() or
  Uninstall() do.
BSolver::VerifyInstallation(): Add flags parameter

Only flag ATM is B_VERIFY_ALLOW_UNINSTALL. It tells to solver to suggest
uninstalling packages when necessary instead of considering such a case
a problem.
pkgman uninstall: improve correctness

... with respect to inter-installation-location dependencies. E.g.
uninstalling a package from common should only uninstall packages
depending on it, when system doesn't still provide those dependencies.

We don't consider uninstalling packages from more specific installation
locations when dependencies are uninstalled from a more general one yet.