pacman: implement universal transactions

This allows using -S, -U and -R in one command:

pacman -S foo -R bar

To make this work some breaking changes have made.

Targets have to come after the operation:

pacman -S foo  //works
pacman -Syu    //works
pacman -yuS    //works
pacman foo -S  //doesn't work

This could be supported with some code to copy all targets before the first operation into the first operation's target list.

And -u as a short for --unneeded has been removed as it conflicts with --sysupgrade. However as -u/--sysupgrade is bound to -S, accidently doing pacman -Ru will not accidently cause a system upgrade.

Another quirk with the UI is that -S has many non transaction related flags, -Sc -Sg -Sl -Si. These have been split off as "sync only" flags. Meaning they show up with pacman -Si foo but will be invalid on pacman -R bar -Si foo.

Also when -R'ing and -S'ing the same package in some command it's treated as a full uninstall then reinstall. The backup files are .pacsave'd and the install reason is set to explicit. I feel like this behavious is good. This also allows you to wipe config files which is what --nokeep was intending to solve.

Other flags just have to have the op they belong to to be used for them to be valid.

For example:

pacman -Rn foo //works
pacman -S -Rn //works
pacman -Sn    //doesn't work
pacman -Sn -R //works

We could posibly drop these flags belonging to each operation and just make them generic transaction flags.

Implements FS#9694

Signed-off-by: morganamilo <morganamilo(a)archlinux.org>