Doc: Improve SQL Example: Master Detail Example

• The entire text on the example landing page is "The example also shows how to add as well as remove data from both the database and the associated XML file using the API provided by the Qt SQL and Qt XML modules, respectively.". The preamble from the example listing page is missing, so the text seems completely out of context (this is a known issue when generating this part of documentation). As this is the only text available, it makes the entire example come off as unfinished.
• Column titles in the application are all lower-case (i.e. "title", "artist", "year").
• Detail view uses Title Case for "Number of Albums".
• Detail view and album covers is a (or an outdated?) promotional poster for Qt. A developer who is looking at Qt examples to learn how to use Qt, probably doesn't need to be sold on the idea that they should consider Qt in the first place (this is like online advertising algorithms that pitch the product you just bought). Maybe make the content more relevant (e.g. pitch use-cases, rolling ads for upcoming Qt events, relevant and related feature highlight).
• Displaying a text about the example in Help->About is a nice touch and should be replicated in other example applications.

See also:

• https://wiki.qt.io/Examples_Revamping_Qt_SQL#Notes
• https://wiki.qt.io/Examples_Revamping_Qt_SQL#Examples