Add upgrade by using only the SAT core

- Adds upgrade --universe and upgrade --universe --clean. It will
  attempt to bring the system as much close as the content available in
  the repositories. It differs from a standard upgrade which checks
  directly that what is pulled in doesn't conflict with the system. In
  this new way, we just query the SAT solver to decide that on our
  behalf.
- Add uninstall --full-clean. It uses only the SAT solver to uninstall
  the package and it will drop as many packages as required (including
  revdeps of packages too.

cmd/upgrade.go

@@ -60,6 +60,8 @@ var upgradeCmd = &cobra.Command{
 		force := LuetCfg.Viper.GetBool("force")
 		nodeps, _ := cmd.Flags().GetBool("nodeps")
 		full, _ := cmd.Flags().GetBool("full")
+		universe, _ := cmd.Flags().GetBool("universe")
+		clean, _ := cmd.Flags().GetBool("clean")
 
 		LuetCfg.GetSolverOptions().Type = stype
 		LuetCfg.GetSolverOptions().LearnRate = float32(rate)
@@ -69,11 +71,13 @@ var upgradeCmd = &cobra.Command{
 		Debug("Solver", LuetCfg.GetSolverOptions().String())
 
 		inst := installer.NewLuetInstaller(installer.LuetInstallerOptions{
-			Concurrency:   LuetCfg.GetGeneral().Concurrency,
-			SolverOptions: *LuetCfg.GetSolverOptions(),
-			Force:         force,
-			FullUninstall: full,
-			NoDeps:        nodeps,
+			Concurrency:                LuetCfg.GetGeneral().Concurrency,
+			SolverOptions:              *LuetCfg.GetSolverOptions(),
+			Force:                      force,
+			FullUninstall:              full,
+			NoDeps:                     nodeps,
+			SolverUpgrade:              universe,
+			RemoveUnavailableOnUpgrade: clean,
 		})
 		inst.Repositories(repos)
 		_, err := inst.SyncRepositories(false)
@@ -109,6 +113,8 @@ func init() {
 	upgradeCmd.Flags().Bool("force", false, "Force upgrade by ignoring errors")
 	upgradeCmd.Flags().Bool("nodeps", false, "Don't consider package dependencies (harmful! overrides checkconflicts and full!)")
 	upgradeCmd.Flags().Bool("full", true, "Attempts to remove as much packages as possible which aren't required (slow)")
+	upgradeCmd.Flags().Bool("universe", false, "Use ONLY the SAT solver to compute upgrades (experimental)")
+	upgradeCmd.Flags().Bool("clean", false, "Try to drop removed packages (experimental, only when --universe is enabled)")
 
 	RootCmd.AddCommand(upgradeCmd)
 }