Use more standard button code
This commit simplifies the button code for Elisa in the following ways:
- Use ToolButtons rather than flat Buttons for controls than want to look like ToolButtons. This is possible now that our QQC2 style shows ToolButton focus correctly.
- Remove hardcoded custom button sizes and let them be their natural size so they adjust with the scale factor and font size properly.
- Make HeaderFooterToolbar a bit smaller to fit the new noew-smaller ToolButtons.
- Redo the custom contentItem for the sort button to work properly with standardized buttons.
Everything looks pretty similar, but the buttons and toolbars are all a little bit more compact now:
Everything I tested still works, and the test still pass.