feat(i3status): new applet to embed i3status in panel/dock

[jokeyrhyme]

• this PR adds a new applet that serves as an adapter for processes that implement the i3bar protocol ( https://i3wm.org/docs/i3bar-protocol.html )
• this might make COSMIC more desirable for folks who are coming from i3/sway and already have their bar setup exactly the way they like it
• it could also serve as an alternative path for applet development, for folks who aren't yet comfortable with Rust but are able to produce JSON streams, etc

my example i3status-rust setup running in swaybar:

the same example running within this new COSMIC applet:

must-haves:

• launch a real i3status-rs process and subscribe to its stdout
• parse the stdout lines into COSMIC text widgets
• bike-shed a much better name (I3status in code irritates me so much, haha)
• applet icon
• sort out error handling
• use the same font/size as the time/date applet
• support auto-detection of i3status and i3status-rs executables
• support basename-only commands by searching PATH (using which ?)

follow-up items (future PRs):

• provide a GUI for users to configure the font/size
• figure out what to do with pango-versus-nomarkup
• provide a GUI for users to add their own preferred command (e.g. a custom executable built with barista)
• feed user clicks through to i3status process

[jokeyrhyme]

Bahaha, okay, I just noticed #92 which may be more sophisticated than my effort, but I take this as validation that I'm not the only person on Earth who wants this feature to exist :)

[ryanabx]

Bahaha, okay, I just noticed #92 which may be more sophisticated than my effort, but I take this as validation that I'm not the only person on Earth who wants this feature to exist :)

That PR is pretty old, at the very least it's good to have an up-to-date version of it. If it looks like Ian's version is more robust though, maybe you could rebase his PR to get it up to date.

[jokeyrhyme]

Yep, I finally have a few hours to spare, so I'm going to branch from the other PR (to preserve the authorship of those commits) and then work through the checklist I have in this PR and see where I end up

[jokeyrhyme]

Closed in favour of #360