Move state handling into the webserver

[sabeechen]

The main goal of this PR is to fix issue #12, which it accomplishes by making the webserver report its current state (busy, command, etc) through a simple JSON API, so the browser is no longer responsible for determining when the printer is working. This also allowed me to do some refactoring and simplification where it made sense in the context of my changes. In particular I've:

• Removed the delay(500) from state changes (on the esp32) since the web-ui no longer requires it to show a consistent state.
• Consolidated the javascript logic that disables/enables input controls based on the "busy" state into a single method (to avoid duplication)
• Moved the UI properties for #progress-bar and #size-helper from javascript into CSS (they get changed based on data attribute selectors)
• Changed as much http request-based javascript as possible to use promises (ie the async/await/fetch syntax).
• Changed the javascript status polls to only make a new request after the previous one finishes, which prevents requests from queuing up and hammering the webserver during transient disconnections.
• Simplified the web server init code, which required updating the AsyncWebServer dependency.
• Added some TODO's for areas where I intend to add funtionality later

To the best of my ability this makes no change to the appearance or effective styling of the web interface. One benefit of this PR is that if the page is refreshed while printing its printing status will still be reflected after the refresh, ie preventing you from submitting a label until the previous one finishes. In such a case it won't show the proper label text, but I intend to address that in follow-up PR's as it requires more substantial refactoring to be done cleanly.

[sabeechen]

Apologies there were some upstream changes I neglected to merge into this PR previously, this one should be good to review.

[andreisperid]

Hey @sabeechen, great improvements, I've been testing and it seems super stable... Thank you very much!

I just noticed that while the music is playing the web app progress is 99%, it was a simple fix (32c6777b2d946535ac10cd0f4a1ddee7f458fe8f).

PS: I guess my auto format just changed a lot of formatting underneath, but it is just line 225.

[sabeechen]

What are you using to auto-format? I'll make sure I use the same mechanism.

[andreisperid]

I'm using prettier for VS Code with the standard settings. What about you?

[sabeechen]

Wasn't using anything (just trying to match style), but I'll start using prettier. I just want to use the same thing you're expecting.