This (partially) reverts commit 127bbdf653.
Only incorrect changes from Kirigami.Units.largeSpacing to
Kirigami.Units.gridUnit are reverted. Only Plasma.Units were buggy.
Adds an experience for users on first login, allowing some basic configuration.
This is separate from a first start wizard, which would run as a separate user with elevated permissions, and include options that an installer would have.