transactions: Major rewrite of step generation

transactions: Major rewrite of step generation

When we extract from libsolv what steps we need to perform in order to
apply the changes to our system, there was a problem that when updating
packages, the previous version was not properly removed from the
database.

This has now been fixed by adding additional steps which are passive and
will remove the left-over metadata.

This should hopefully make the entire process more robust and easier to
handle in the code as each step has one simple job to do.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>