checkbox-touch: add confirmation dialog component

This patch adds a component asking user for confirmation.
checkbox-touch: add app-wide settings

This patch brings app-wide settings in form of a dictionary stored in mainView
object. Should any page want to store settings it may reference
mainView.appSettings[key] to do so. It's particulary useful if pages are
created dynamically.
checkbox-touch: add confirmation dialog logic

This patch introduces logic responsible for creating popup dialog, displaying
it and storing user's preference regarding whether to ask that question again
in the future.
checkbox-touch: use confirmation dialog when skipping tests

This patch makes checkbox-touch show 'are-you-sure' kind of dialog when user
chooses to skip test.

Fixes: https://bugs.launchpad.net/checkbox-touch/+bug/1382970
Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
"automatic merge of lp:~kissiel/checkbox/skip-confirmation/ by tarmac [r=sylvain-pineau][bug=1382970][author=kissiel]"