Fixed offset for overlay in moveable TableViewColumns

The Loader needs to be reparented in order to draw the overlay on
top of everything. In addition we need to take both the item offset and
the contentX into account. Note I also tweaked the actual drop offset
by headerRowDelegate.width/2 as that feels a bit more balanced.

[ChangeLog][QtQuickControls][TableView] Fixed an issue with
the header overlay offset while re-arranging TableViewColumns

Task-number: QTBUG-37180
Change-Id: Ia80049616bb30e1391948fdeaf3f8d68afd7ce3e
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Styling improvements for Calendar

Also
- added the property Calendar::frameVisible.
- moved the gridVisible property to CalendarStyle

Change-Id: I57da65af130098ac5d0b858c9f964e52e3ba6922
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Label should use SystemPalette.windowText

In themes with inversed colors text and windowText colors may differ,
and Label as QLabel's analog should use the correct one

Task-number: QTBUG-37468
Change-Id: Ie4f574e782b1c9274d86f45433c36ecab2989b97
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Menu: Estimate item height from first visible item

The first item could be hidden, or not a normal item,
thus returning an unproper height. The consequence in
the reported issue being that the popup's maximum height
would be that of a scroll indicator.

Task-number: QTBUG-37445
Change-Id: Ib06d25643cd11224d5eab0452dadd0f6d4119fb9
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Menu: Improved sloppy menus logic

Instead of relying on fixed angles, we now test that the current
mouse position is in the triangle defined by the previous mouse
position and the submenu's top-left and bottom-left corners. The
sloppy timer duration has also been increased to 1s.

Change-Id: I575346ac20b5da68ab8ebd6e3cf9a6ddba2b7a72
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Merge remote-tracking branch 'origin/stable' into wip/tizen

Change-Id: If257dabf080cce3811f0aa2b8bba7154bb653c67