TableView: Reset dragged header position if not moved

The user expects the "ghost" header to be aligned with the actual
column header when he starts dragging it.

Change-Id: Ifccf633403a72fe8448132fe6c349a85acba28d7
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
TableView: Make sure we get the content width with hidden header

The key is to get a headerRowDelegate of non-null dimensions.

Task-number: QTBUG-39393
Change-Id: I5ceadb07ebfc84142bbbfe98c5d61780e0314cf5
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Menu: Properly relay enabled state to QPA menu object

Task-number: QTBUG-39384
Change-Id: I1b71912b4f35ea0aa9e06667a5c0ecedec30f980
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
TableView: Allow resizing and scrolling single-column tables

Also makes sure the resize handle is visible in desktop style.

Task-number: QTBUG-39393
Change-Id: I44410c65e76b0a3221ea5fce713c1f1b69079947
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Merge remote-tracking branch 'origin/stable' into 5.3

Change-Id: Ib60d7e00639f5a73bf4eed48e44dab880cdc748b
Merge "Merge remote-tracking branch 'origin/stable' into 5.3" into refs/staging/5.3