Accessibility fixes

[plousia]

Accessibility issues to be fixed:

-tabs lack correct tab markup/roles
-tabs lack correct tab keyboard behaviours
-need a wrapper element around the rest of the element with the "tabpanel" role (this one is a little weird because it's not switching between two different pieces of content, but showing/hiding some pieces, but one tabpanel shooooulllld work I think)
-"other amount" behaviour:
-there is a tabstop at the "other" radio button. Tabbing forward from a set of radios should focus the next focusable element after them, instead it selects the "other" radio. Only arrow keys should navigate between radios in a set.
-Initially, tabbing forward from the radio buttons skips over the "other amount" text input. It's possible only to shift + tab back to it. Once it's been focused, it's possible to tab back to the radios and tab forward to it.
-when using the mouse, you have to click twice to focus the "other" text input. First click selects the "other" radio, second click focuses the input.
-it can't be assumed that because someone clicks or focuses the "other" text input, they want to contribute another amount. "other" radio should only be selected when someone enters an amount in the text input. Even so, this whole interaction is pretty dicey as it's taking control away from the user (changing input in one form element based on the state of a second). It might be better to hide the "other" text input until the "other" radio is selected, then reveal it and make it required. When a different radio is selected, hide and unrequire it again.
-no error message for empty "other" input when form is submitted with "other" radio selected but no amount in other input

[adixon]

Thanks for this. And yes, the other amount behaviour has always been a bit of a mess.