Resources including Linux icon, desktop file and AppStream metainfo

[redtide]

Misc request about resources:

• Graphic resource directories looks a bit fragmented and there is a empty resources folder: is it planned for a change or can I propose something different?
• I would like to add a desktop file for the standalone, an icon that can be extracted from mac .icns or windows .ico (or if there is a svg/png that I can use)
• Add an AppStream metainfo xml file (used by some graphic package managers or AppImages)

[falkTX]

* Graphic resource directories looks a bit fragmented and there is a empty resources folder: is it planned for a change or can I propose something different?

The resources dir is used for building the web version. The files used are quite large so I ended up not placing them in the repo. I am okay with just deleting the whole folder

* I would like to add a desktop file for the standalone, an icon that can be extracted from mac .icns or windows .ico (or if there is a svg/png that I can use)

A desktop file would be much welcome, but needs to be integrated into the install procedure to be useful I guess..
@spunktsch can likely provide an svg for the icon

* Add an [AppStream](https://freedesktop.org/software/appstream/docs/chap-Quickstart.html) metainfo xml file (used by some graphic package managers or AppImages)

AppStream requires to keep the changelog and last release version on the xml file, which I don't think it is a good idea as it gives extra work to project maintainers and can't be automated in a non-spec-breaking way. So I am typically against it, as I already had the case in Carla where distros end up tweaking the AppStream xml file so they might as well generate it themselves..

[redtide]

for the resource folder, if needs to be deleted to be used for other purpose then I could use a different one, say res or artwork?

I can include the resource changes in a first PR, adding in a second one the cmake install section, or just all in one PR, as you like.

the releases section is not mandatory, I never add it for the reason you said, it's good to have the metainfo for some information and screenshots instead.

[falkTX]

Put desktop file in utils, icons can go in graphics if they are meant to be used by the runtime plugin or also in utils if it is a system-level integration thing alike macOS and Windows.
So I think all the files you mention go in utils

[falkTX]

FYI the resources dir is now gone from d8d4585 on