This moves all the "default" margins of the welcome pages into a single point (the WizardPanel)
in order to prevent having to re-define it every time.
I've also fixed some incorrect margins that we had
CURA-6057
Use the wide margin instead. It's practically the same, nobody is going to notice. It still looks spacey and nice, and it's more consistent with the rest of the interface.
We had previously agreed that we will not make any new widget-specific theme entries any more.
Contributes to issue CURA-6057.
On some operating systems the text would not fit due to different font rendering. Also, after translation, it probably wouldn't fit either.
Usually we have the button size adjusting to the text inside it. The design didn't do this, either because it was too difficult to do in Zeplin, because the designer was lazy, or because the designer didn't know that this was the normal style in the rest of Cura. And the programmer took that over literally.
Contributes to issue CURA-6057.
