Add category classes for the model to make it tidier and easy to
extend (i.e. adding more categories).
Change-Id: Ied8641802f600c5cb0b036aba6ad44dbde612a09
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Also some relevant tweaks.
Change-Id: I7bace9ce6bd7b45951cc18f7175b4646251196f0
Reviewed-by: Ali Kianian <ali.kianian@qt.io>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>