Preparing for GTK+3.10

This also removes an errant HAVE_GRANITE preprocessor macro that
should've been removed a long time ago.
Remove Gtk.Notebook from Accounts dialog: Closes bgo#713955

Replaces Gtk.Notebook with Gtk.Stack, remove various Notebook hacks
we had to introduce.
Gtk.HeaderBar for main window and composer toolbar: Closes bgo#713478

Nice code reduction using Gtk.HeaderBar in place of Gtk.Toolbar.
Main window no longer has chrome but composer window still does.

Conflicts:
	src/client/components/main-window.vala
	src/client/components/pill-toolbar.vala
	src/client/composer/composer-toolbar.vala
If Folder's display name changes, signal so UI can update

Noticed this while working on Gtk.HeaderBar patch, that if the display
name changes it won't be reflected in the UI.

Conflicts:
	src/client/components/main-window.vala
	src/engine/abstract/geary-abstract-folder.vala
Display total count, not unread, in headerbar for Drafts/Outbox

This is a similar heuristic as in the folder list, as unread counts
in these folders is uninteresting.
--enable-unity flag to deal with GtkHeaderBar issues: Refs bgo#727624

Unity doesn't deal well with pure GtkHeaderBar apps, so this allows
for the GtkHeaderBar to be treated like a toolbar and the window
retain its chrome.
Improve appearance under Unity: Closes bug #727624

Toolbar improvments, primarily by removing label outright and letting
icons do all the work. Also, from some user request, have tried
moving icons to right side of toolbar, where they're closer to
the conversation viewer.

This does not fix dragging the window by the toolbar (that's fixed
in 3.10, bug #709914) or the title/subtitle in the GtkHeaderBar
being too close. We might consider using a custom title widget.
Regression: Search upgrade prog monitor not shown
Update GTK requirements in debian packaging
Fix endless retry loop when selecting unselectable folder

Discovered when selecting the [Gmail] folder, which is unselectable.