classes.app: Set icon, desktop file

[ferdnyc]

Do a couple of things to establish our application identity with various window managers, desktop session managers, etc

Fixes: #1112

[SuslikV]

from images import openshot_rc - is excessive check.

It seems that it works for Windows without changes. Thus, all OK.

[ferdnyc]

@SuslikV

Cool, thanks, I was pretty confident it was cross-platform.

from images import openshot_rc - is excessive check.

Not sure what you mean -- that import establishes the resource file for the application. When I later use QIcon(":/openshot.svg") to set the window icon, that import is what makes the :/... path resolve to the resource file.

The resource file does end up registering as an unused import, annoyingly, but that's just how PyQt set things up.