This patch introduces the HeaderView class, which is a widget that
implements the column headers of TableView and TreeView.
This greatly simplifies event management in the view implementations
and also makes it much easier to eventually implement row headers.
Instead of SortingProxyModel having a column+order, we move that state
to AbstractView. When you click on a column header, the view tells the
model to resort the relevant column with the new order.
This is implemented in SortingProxyModel by simply walking all the
reified source/proxy mappings and resorting their row indexes.
.. and make travis run it.
I renamed check-license-headers.sh to check-style.sh and expanded it so
that it now also checks for the presence of "#pragma once" in .h files.
It also checks the presence of a (single) blank line above and below the
"#pragma once" line.
I also added "#pragma once" to all the files that need it: even the ones
we are not check.
I also added/removed blank lines in order to make the script not fail.
I also ran clang-format on the files I modified.
A MultiView is a combination of ItemView, TableView and ColumnsView
smashed into a single widget. You can switch between the view modes
by calling MultiView::set_view_mode().
Note that MultiView inherits from StackWidget, not AbstractView.
That's purely for practical reasons, although I'm not entirely sure
if there would be some benefit to having it inherit from AbstractView.
