Put properties in a modal dialog

With some UI transitions removed during the port away from clutter, its
better to have it in a dialog.

Known issues:

* Our snapshots UI relies on disabling all controls to get out of the
  snapshots view while an operation is in progress. We lose most of this
  ability to disable all controls with this patch. We really shouldn't be
  doing this anyway so lets actually solve this issue after these UI
  rework changes are merged into git master.

* This implies that now we can't change name of machine through title
  anymore. Main reason is that there seems to be no way to set a custom
  widget as title of a dialog but I don't think many will miss this
  feature anyway, especially now that its a dialog.

* Page titles are missing in the sidebar when coming to properties from
  wizard and hence the ability to switch pages. However, this is no
  longer an issue when we later drop the sidebar all together.

https://bugzilla.gnome.org/show_bug.cgi?id=733367
Drop now redundant PropertiesToolbar

https://bugzilla.gnome.org/show_bug.cgi?id=733367
Drop now redundant Sidebar class

https://bugzilla.gnome.org/show_bug.cgi?id=733367
mini-graph: Adjust for bigger size

We are about to put mini graphs into properties' main view (and then
remove them from sidebar), where they'll need to be much bigger than
they currently are.

TODO: Make them look good on bigger size as well.
i-properties-provider: Add Property.flushed signal

Add a signal to Property to notify interested parties that said property
has been flushed.
libvirt-machine-props: Add resource stats graphs

Add resource stats graphs to properties under 'System' page.

This is part of move of sidebar contents to main view before sidebar can
be dropped.
libvirt-machine-props: Refactor system props code a little

Put all the code to add troubleshoot log button and dialog into a
separate method.
libvirt-machine-props: Change placement of troubleshoot log

Put the troubleshoot log button between resource stats and resource
controls, as per new UI mockups.
libvirt-machine-props: Add 'Force Shutdown' button

Add'Force Shutdown' button to properties under 'System' page, next to
'Troubleshooting log' button.

This is part of move of sidebar contents to main view before sidebar can
be dropped.
properties: Turn it into Gtk.Notebook from Gtk.Stack

According to the new UI mockup, we need it to be a notebook so that
we have page switching controls before we drop the sidebar.
Drop PropertiesSidebar

Drop the sidebar from properties. It looks weird now in the dialog and
all the functionality it provides has already been replaced by previous
patches to this.
properties: Specify min content size on ScrolledWindow

If minimum width and height are not set, ScrolledWindow hides most of
the content.