Refactor archive loading

Ark currently loads an archive by using `Archive *Archive::create()` first
and then `ListJob *archive->list()`. If an archive property is read
*before* list() is called, the archive is listed in the background with
listIfNotListed().
This design is responsible for a lot or problems (see T1877, T3296 and T330).

This commit refactors ListJob in a new LoadJob class. Is not possible
anymore to create an archive and then list() it. Instead, a LoadJob is
started first and then the archive can be retrieved at the end of the
job.

Differential Revision: D2811