[Development] New Qt example development guideline and revamping examples

[Tor Arne Vestbø]

> On 18 Jan 2023, at 13:12, Giuseppe D'Angelo via Development <development at qt-project.org> wrote:
> 
>> RECOMMENDED
>>    Prefer signal/slot connection with lambdas: https://doc.qt.io/qt-6/signalsandslots.html
> 
> All the contrary, do NOT do that, as it results in 200+ lines unnamed lambdas. Strongly prefer named slots. Keep the lambdas short and to the point. Do not use unnamed lambdas.

No, strongly prefer lambdas if they are within a reasonable size. No-one is arguing for 200+ line lambdas.

Tor Arne