Popup widget position recalculated if parent widget resized

The ctkPopupWidget resides in its own window that should follow the
application window while it is being moved or resized. (This matters
only if the pop-up widget is pinned to the application window,
otherwise it is not visible during moving or resizing.)

This commit corrects the calculation of the new window position.

Fixes #411.
Fix popup offset when top-level widget is moved on mac

See issue #416
Merge branch '416-popup-offset-on-mac'

* 416-popup-offset-on-mac:
  Fix popup offset when top-level widget is moved on mac
Merge branch '411-ctkPopupWidget-put-in-wrong-position-on-resize-or-move' of https://github.com/NifTK/CTK into NifTK-411-ctkPopupWidget-put-in-wrong-position-on-resize-or-move

Conflicts:
	Libs/Widgets/ctkPopupWidget.cpp
Fix ctkDirectoryButton file dialog for AcceptSave mode

In AcceptSave mode, the file dialog shall not accept non-writable folders.
2 mechanisms are in place:
 * a custom QSortFilterProxyModel for display information
 * a smart file dialog that does not allow non-writable folder to be selected
It still fails on Windows for some reasons.

Closes #365
Merge branch '365-reject-non-writable-folders'

* 365-reject-non-writable-folders:
  Fix ctkDirectoryButton file dialog for AcceptSave mode
Disable decimal synchronization by default in ctkSliderWidget

This can lead to unwanted behavior. It should be a conscious choice to
enable the synchronization of decimals
See issue 3642 in na-mic bug tracker
Merge branch '3642-disable-synchronize-decimals'

* 3642-disable-synchronize-decimals:
  Disable decimal synchronization by default in ctkSliderWidget