Doc: Added a section about the controls in the First Steps with QML page.

-added near the top to imply that the controls is a starting point.

Task-number: QTBUG-33595
Change-Id: I31290629dd9bca3c1e477140bc530b8b4b565dba
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Doc: Updated styling QML use case page.

-focused on styling the controls
-removed section about customizing properties (already covered)
-revised the section about SystemPalette

Task-number: QTBUG-33595
Change-Id: I065971fa9ab57e5eacf83077925ccb52c9f9717d
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Doc: Added section about Qt Quick Layouts in the layouts use case page.

-also mentioned that Qt Quick 2.1 is required

Task-number: QTBUG-33595
Change-Id: I5cfd2e478fc16ecca792705d56aaddd614759315
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Doc: Added links to various text-related pages to text QML use case page.

Task-number: QTBUG-33595
Change-Id: I16714ae6a140b2296a54dfc8125056ed856d5420
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>