Use dosbox-staging icon and .desktop tweak

[dreamer]

Use official vector icon instead of raster

Add StartupWMClass to desktop entry to allow users to correlate/override application icon without risk of conflict with other binaries sharing "dosbox" name.

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Hello, @popey :) I did not expect snap package appearing so early, and from a prominent Snapcrafter.

Thank you so much for preparing this package for us! I believe it will be a go-to solution for many, many users - I tested it myself on Fedora and did a quick test on Ubuntu 20.04 - both worked like a charm :)

I will need some time to wrap my head around Snap and how to best integrate it into our CI pipeline (I believe this is intended use-case?) so, for the time being, I left a link pointing to your package on our homepage: https://dosbox-staging.github.io/downloads/linux/

This PR uses our official icon; I am not sure how to point snap package to correctly handle icons for tiny sizes inside snap - we provide a suite of icons that look slightly better at 16px-32px sizes, (although fundamental icon design needs to change to make it really work).

Our icons are here: https://github.com/dosbox-staging/dosbox-staging/tree/master/contrib/icons And a suite of icons in XDG-style directories can be generated with:

[dreamer_@tars icons]$ make hicolor  # requires rsvg-convert
[dreamer_@tars icons]$ tree hicolor
hicolor/
├── 16x16
│   └── apps
│       └── dosbox-staging.png
├── 22x22
│   └── apps
│       └── dosbox-staging.png
├── 24x24
│   └── apps
│       └── dosbox-staging.png
├── 32x32
│   └── apps
│       └── dosbox-staging.png
└── scalable
    └── apps
        └── dosbox-staging.svg

Outside of this PR:

There are some other tweaks, that I think would benefit users, although they might trigger some edge cases, and I don't know yet how snap handles them (e.g. it would be preferable if dosbox command invoked application instead of dosbox-staging), but I leave them out for later.

Thanks again! :)

[popey]

I've triggered builds, and have updated the icon in the store. These will ripple out to users shortly.

I'd be happy to hand this snap over to you once you have it all setup in CI. Also happy to help you guys implement that, when you have time. Having the dosbox name might be tricky, as the "official" application has that, but we can have the conversation on the snapcraft forum, if you'd like.

[popey]

@dreamer Let me know if there's a place I can hang out (discord / forum / slack / irc / whatever) so we can discuss further progress. Happy to lurk and answer questions as needed.

[JoshuaFern]

The official Discord is at https://discord.gg/8mFhUPX