Retrodeck support

[pawndev]

This is the continuation of #213

Next things to think of:

• If grout is a component of retrodeck, needless to create a gamelist.xml in port for that ?
  • Surely we can omit this part
• games downloaded and media in gamelist.xml in the roms folder doesn't seems to be read by retrodeck
  • because they does not go in the roms folder, but in the $XDG_CONFIG_HOME/ES-DE/gamelists/{core}/ folder
  • make sur to not override something else (e.g. alternateEmulatore)
  • same for images/videos/etc, paths: $XDG_CONFIG_HOME/ES-DE/downloaded_media/{core}/{3dboxes, backcovers, covers, fanart, manuals, marquees, miximages, physicalmedia, screenshots, titlescreens, videos}
  • can we put absolute path in the gamelist.xml ?
  • the medias does not seems to appear in the gamelist.xml when scrapped from scrapper, not mandatory ? (only fields: path, name, desc, rating, releasedate, developer, publisher, genre players)
• how to retrieved the path where the roms/saves/bios folders are ?
  • In the $XDG_CONFIG_HOME/retrodeck/retrodeck.json there are many paths defined

Next things to do:

• get paths from retrodeck.json
• remove grout gamelist from port
• Change grout log path
• change gamelist path to $XDG_CONFIG_HOME/ES-DE/gamelists/{core}/
• change medias downloaded (in the actual version, we can't download all, we need to choose which art to get)
• do not fill all gamelist field like other ES cfw integration (cfw options on which field to allow, and not filled will be all ?)
• Once AmberElec PR feat(CFW): added AmberELEC support with RG351V and Rg351P devices #234 is merged, get the relative path function for gamelist

Initial description:

Adds initial support for RetroDECK, so it can be added as a non-Steam game.
Feel free to request any change, especially if I forgot something.

This is a follow-up of this issue: #210.

EDIT: Added associated documentation.

EDIT2: Got inspired and added an automatic install script with media, so it looks nice in the Steam game library.

It currently looks fine on Bazzite, but I have an issue with nonsteam not detecting the Steam install on SteamOS. I'll investigate when I have a bit more free time.

[XargonWan]

Note: in RetroDECK users can move the folders, so better to read their location from the retrodeck config (json format).

[pawndev]

Note: in RetroDECK users can move the folders, so better to read their location from the retrodeck config (json format).

Yep I already did the parsing of the config json in my local changes