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.