"Waiting to install" for ever - Ubuntu Software - 16.04

Install .deb packages from the terminal:

$ sudo dpkg -i <path/to/deb.deb>
$ sudo apt-get install -f

The reasoning behind apt-get install -f from the man page:

 -f, --fix-broken
           Fix; attempt to correct a system with broken dependencies in place. This option, when used with install/remove, can
           omit any packages to permit APT to deduce a likely solution. If packages are specified, these have to completely
           correct the problem. The option is sometimes necessary when running APT for the first time; APT itself does not allow
           broken package dependencies to exist on a system. It is possible that a system's dependency structure can be so
           corrupt as to require manual intervention (which usually means using dpkg --remove to eliminate some of the offending
           packages). Use of this option together with -m may produce an error in some situations. Configuration Item:
           APT::Get::Fix-Broken.

_{Credit: Mohit Rajan's comment}

1 - Donwload the old "Ubuntu software center" in the new "Ubuntu software".

2 - unity --reset-icons or Restart your computer (to remove the "waiting to install")

3 - Open the .deb file with the just installed "Ubuntu software center"

4 - Install it