checkbox-touch: add ProgressBox component

This patch adds ProgressBox component that is similar to progressBar, but
provides more flexibility.

Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
checkbox-touch: use ProgressBox throughout Checkbox Touch

This patch places ProgressBox on top of every page that displays test
description on verification screen.

Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
"automatic merge of lp:~kissiel/checkbox/progressbox/ by tarmac [r=zkrynicki][bug=1396018][author=kissiel]"