Add Digital mode for clock tab

[Nekhelesh Ramananthan]

Currently the clock app shows the time in analogue format only. However there are people who prefer the digital format. The clock app should allow for easy switching between these two modes. This is something which is also available in other mobile OS clock apps.

Do note that this bug report concerns only the digital mode for the clock tab and not the alarm, timer or stopwatch tab. They will addressed later in other bug reports.

Difficult: Medium/Hard

---------- Desired Solution ---------------
Currently the clock tab does store a setting option for analogue or digital mode. However it is currently disabled. Enable it and then when in the digital mode the clock tab should show the time in digital format. The font should be big enough to easily readable. Feel free to take design cues from other mobile clock apps.

One thing you need to take care of is that in the analogue form, when you click on the clock center, it shows the sunrise and sunset times. In the digital mode, this must also be possible.

Second thing, you might want to think about using QML loaders to ensure that the analogue clock component does not waste memory while being in the digital mode. This is however not essential and can be addressed in a separate MP if necessary.

Also additional points if the digital text changes color while the mouse cursor hovers over it to indicate that it can be clicked/pressed in desktop mode :)