Add desktop files, resize desktop icon, and metadata.

[kevinsmia1939]

Related Issues

Previous noticed for Flatpak mentioned here: #11777

Purpose

Hi,
In the effort to package OpenModelica as Flatpak here: #11777
I add an 256x256 icon of omedit and notebook which is simply a resized of 300x300 omedit.png using imagemagic.
The notebook icon is converted from .ico in GIMP into .png.

I create a desktop file which will serve as a desktop icon for Linux distro.
I also create a metainfo file which will be use to display information about openmodelica on a software store front such as Flathub which I will submit to.

At the moment, I am not certain where should I place desktop file and metainfo file in the directory. Let me know a better place for it.

I will be keeping openmodelica on Flathub update, but ideally, one of the main developer from openmodelica should have access to the Flathub git repo as well. So I try to invite someone when I submit a pull request to Flathub.

Here are general info on metainfo file: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html
Flathub: https://flathub.org/
Publishing on Flathub: https://docs.flathub.org/docs/for-app-authors/submission

[CLAassistant]

All committers have signed the CLA.

[adeas31]

This is more for @sjoelund to review.

@kevinsmia1939 take a look at https://github.com/OpenModelica/OpenModelicaBuildScripts repo. We already have .desktop files.