[clock app] Timer format should read mm : ss and count upwards into minutes and hours

[Calum Pringle]

When setting a timer, the initial visible fields being edited should be the minutes a seconds only (currently hours are shown too).

When turning the dial past 59 seconds or minutes, the timer should continue to keep adding up past 1 hour, or 1 minute.

For example

00:59 becomes 01:00

59:59 becomes 01:00:00 (hours are always associated to minutes, there is no possibility to add hours directly other than by counting up from minutes)

-- This is invalid or at least hard to verify, current clock app has no timer ---

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:ubuntu-clock-app at revision 40, scheduled for release in ubuntu-clock-app, milestone alpha-1