Accessibiity

[aarongustafson]

Fixes #121 by

1. Making the buttons actual button elements (which are focusable, interactive with keyboard & mouse)
2. Handling the show/hide behavior in an accessible way
3. Adding appropriate ARIA labels
4. Added a "timer" role to the timer showing the elapsed recording time
5. Swapping out the "stop" icon being used for the "discard" action with a trash can that make the intended action more obvious for sighted users (users are not "stopping" the recording, that’s what the pause button does).
6. Maintain focus on the first button when opening the component
7. Ensuring the buttons are consistently & appropriately sized

Cleanup included removal of CSS that was no longer needed.

From a UX perspective, I still wonder if it might make more sense to have the "save" button be at the end of the component when it’s open, but that’s debatable and secondary to the purpose of this PR.