Draft: Updating application utility to fix integration issue with Pamac and segfault on Gnome

see also: manjaro-hello#43

Fixing issues with doubleclick on package as appstream integration was dysfunctional.

I did not want to dive into appstream issues and the relevant code has been removed (sorry @papajoke).

I also found that in some scenarios packages would not install. I traced this to the default package database (default.json) still referencing packages no longer in the repo. The list has been checked and updated.

To prevent an all out failure because one package is no longer available - and the possiblity having the same issue in the future - a check has been added to validate if a package exist in the repo or not.

The check is made using Pamac backend and this may slow down the selection a tiny bit.

If not the package description in app browser changes to {{pkgname}} is no longer available and the checkmark is removed.

Code has also been reformatted and trailing blanks removed.