Add VSCodium logo to the presence.

[AngelCMHxD]

This has been previously discussed on #260 but at that time {appname} (now {app_name}) still returned VS Code while using VSCodium but now it actually returns VSCodium as shown below. This should make using the VSCodium logo as easy as uploading it to the discord application as an asset. This also applies to the Insiders version of VSCodium.

How it's displayed now:
VSCodium Stable:

VSCodium Insiders:

VSCodium Stable logo: https://github.com/VSCodium/vscodium/blob/master/icons/stable/codium.svg
VSCodium Insiders logo: https://github.com/VSCodium/vscodium/blob/master/icons/insider/codium.svg