Fixes

Fixes #989 by @zackkrida

Description

This PR automatically focuses the filters sidebar when the user presses Tab key when the Filters button is pressed.
I will also add automatic focusing of the sidebar when the button is clicked. Do we really need this? I think to add it, we would need to do something like Vue.nextTick, because when you click the filters button, the sidebar is not yet rendered.
When the user presses Tab key when on the last focusable item on the sidebar, the focus moves to the first focusable element in the main element. When the user pressed ShiftTab on the first focusable element in the sidebar (whether it's a checkbox or the 'Clear filters' button), the focus goes to the Filters button.

Also, when the user presses Tab on the last focusable element in the main search page (one of the Meta Search buttons, or the scroll to top button), the focus moves to the first focusable element in the layout instead of moving to the filters sidebar again.

Testing Instructions

Open the app on desktop. Try Tabbing from the Filters button, and tabbing through the filters sidebar to the main element. Try All content, Image and Audio views.

Checklist

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