widget: graph: NetGraph: fix unhandled exception

If Qtile trys to come up without default route, this TraceBack appears:

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/qtile-0.8.0-py2.7.egg/libqtile/confreader.py", line 54, in __init__
    config = __import__(os.path.basename(fname)[:-3])
  File "/home/fsc/.config/qtile/config.py", line 139, in <module>
    widget.NetGraph(**widget_graph_defaults),
  File "/usr/local/lib/python2.7/dist-packages/qtile-0.8.0-py2.7.egg/libqtile/widget/graph.py", line 285, in __init__
    self.interface = self.get_main_iface()
  File "/usr/local/lib/python2.7/dist-packages/qtile-0.8.0-py2.7.egg/libqtile/widget/graph.py", line 321, in get_main_iface
    routes[0]
IndexError: list index out of range

Signed-off-by: Florian Scherf <fscherf@gmx.net>
add new layout for vertical monitors

Signed-off-by: Florian Scherf <fscherf@gmx.net>
layout: VerticalTile: add margin support

Signed-off-by: Florian Scherf <fscherf@gmx.net>
Check the results of ConfigureWindow requests

This fixes a similar issue that 71a8d0d04602c53dd05e15a3cf8dde0a00e1fc97 does.
In some cases, we have 'dead' windows that we attempt to operate on. If we just
send unchecked requests, we get the exceptions back in the poll loop and
they're rendered in the users' logs. Instead, we should check them and fail
immediately. The previous patch changes the logging scheme slightly so that
these kinds of errors are not rendered.

Closes #539
Revert "Check the results of ConfigureWindow requests"

This reverts commit ac1ba76579aea05128199e92fc2d3411c912f0f7.

As is noted in #551, this breaks several things and was committed mostly by
accident. We still want this patch, it just needs more work.
Skip test_resize and test_resize_

We have an open issue for skipping these (#509), and peoples' PRs are failing
(and the build is failing) because of them. We should just ignore these tests
until someone actually fixes them.
Add pypy3 tests to Travis