QTreeView makes columns movable except for the first one
(since Qt 5.0, see commit e0fc088c0c). This is indeed best
for actual trees, but not when using QTreeView as a flat
multi-column list (with no "root decoration"). Then it should
be possible to move the first column.
[ChangeLog][QtWidgets][QHeaderView] Flat treeviews can now allow
the user to move the first column (like in Qt 4.x) using the new
method QHeaderView::setFirstSectionMovable().
Change-Id: I6b5025e40850bf5c4c373124ee81f657f3f09d29
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
