Improve Accessibility

[rashfael]

Currently venueless is barely to not accessible, which is obviously big time bad.
Here follows an attempt to find and break apart problems and propose solutions.

Let's divide the broad target of "accessibility" into something more concrete:

Keyboard Navigation Accessibility

Make venueless controlable with ONLY keyboard
This also greatly benefits screen reader users, so I won't list things twice.

• trap focus inside dialogs
• things that show on mouseover should show on focus (like video controls)
• make rooms sidebar arrow key navigable and use tab for bigger regions
• make chat log keyboard/arrow key navigable
• add keyboard shortcuts for quick nav (and advertise them like slack does)
• highlight focused elements properly

Screen Reader Accessibility

Make venueless readable and interactable with a screen reader

• give every interactive element aria-labels or equivalent information
• hide decorative elements (icons, user avatars when username is present)
• Users should get through the greeting dialog (aria-modal enough?)
• Define enough landmark roles for users to navigate around (already partially added)
• handle live content like chat (how do deal with the conflict of "running video" and "new chat content")
• how to handle the background room, announce the transition?

What is okay to not show screen readers? Is the reaction cloud relevant information? If yes, how would we show that to a screen reader? We probably cannot announce the new reactions every 10 seconds.

Misc

some general accessibility issues which don't fit into the big stories above

• color contrast (we already do that for static things, but customers can choose bad theme colors, and we should warn them when they set badly contrasting colors)

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I'm happy to add more points and am honestly desperate for opinions, since the standards are not really forthcoming with guidelines for highly dynamic apps like venuess. My current plan is: Get inspired by Slack/Discord (which use different ARIA stuff) and perhaps Youtube and some others and test things out with NVDA to the best of my ability.