Add button to clear search input

[seanmturley]

Description

There should be a button the clear the search input so the user can start afresh.

Approach

Unfortunately Firefox doesn't support the "default" approach of simply adding type="search" to the input. This necessitates the addition of an <input type="reset"> to act as a button.

This will require some HTML restructuring and restyling. A decent approximation of how to approach this is the Reddit search bar.

[seanmturley]

Done.

A summary of the work:

• Hid default clear button provided by non-Firefox browsers.
• Added <input type="reset"> as a clear button.
• Added a handleInputReset function to clear the searchTerm and to refocus the search <input>.
• Shifted most styling from the input to the form so it could contain the new button.
• Added logic to remove the clear button unless there's a searchTerm.
• Added CSS to hide the clear button unless the form is hovered or focused.