Set font-size of feedback pane to 16px

The font-size used in the feedback pane is 14px which is less
than the font-size used in the rest of the page. Set this to
16px which is the font-size used in the rest of the page, so
that the text in the feedback pane looks as large as the text in
the remaining page.
Reset error rate to 0 on clicking restart link

Fix a bug in QuickQWERTY which causes the the feedback pane to
display the error rate of the previous practice session even
after the 'Restart' link is clicked.