pep8: fix new pep8 errors
gdk: fix icon too large warning

Setting the pitivi icon on main window and various dialogs produced following warning

(pitivi:18711): Gdk-WARNING **: gdk_window_set_icon_list: icon too large (512x512)

Deletes the 512x512 icon and removes it from the build files.

The warning is only fixed when the correct icon sizes are installed.
Use GtkBox instead of GtkV[H]Box everywhere

Remove H and V from GtkBox, GtkScale, GtkPaned and GtkButtonBox

It is deprecated these days.
GtkAligment is deprecated. Margin names have changed.

* replace margin-left with margin-start

https://developer.gnome.org/gtk3/stable/GtkWidget.html#GtkWidget--margin-left

* replace margin-right with margin-end

https://developer.gnome.org/gtk3/3.13/GtkWidget.html#GtkWidget--margin-right

* replace xalign with halign
* replace ypad by margin-start
Stock buttons have been deprecated. icon names have changed.

https://developer.gnome.org/gtk3/unstable/GtkButton.html#gtk-button-new-from-stock

* use custom buttons
* replace stock-id with icon-name

https://developer.gnome.org/gtk3/3.13/GtkToolButton.html#GtkToolButton--stock-id

update icon names

* use correct gtk menu icon
* zoom-fit-best icon name has changed
* add icon to document-open in startup wizzard
Remove deprecation from dialogs

* add default response
* set_transient_for in about dialog

    https://developer.gnome.org/gtk3/unstable/GtkWindow.html#gtk-window-set-transient-for

* don't use stock buttons
* remove unneeded close callback
Remove various Gtk 3.14 deprecations

remove GtkTreeView rules-hint
https://developer.gnome.org/gtk3/3.13/GtkTreeView.html#GtkTreeView--rules-hint

GtkColorButton needs a GdkRGBA color
https://developer.gnome.org/gtk3/unstable/GtkColorButton.html#GtkColorButton--color

schema has been deprecated use schema-id
https://developer.gnome.org/gio/stable/GSettings.html#GSettings--schema

ImageMenuItem has been deprecated in 3.10
https://developer.gnome.org/gtk3/unstable/GtkImageMenuItem.html#gtk-image-menu-item-set-image

GtkResizeMode GTK_RESIZE_QUEUE has been deprecated
https://developer.gnome.org/gtk3/unstable/GtkContainer.html#GtkResizeMode
Verify all ui files with glade for latest Gtk

  * Replace GtkTable with GtkGrid
  * switch glade files to 3.10 for compatibility
Switch glade files to 3.10 for compatibility
Make schema backwards compatible with Gtk3.10
Set emblem-system-symbolic for menu icon before gtk 3.13
Remove deprecation from dependencies dialog
pitivi: Start using glimagesink as default sink
viewer: Redraw the current frame whenever the drawing area draws

Avoid artefacts when we resize the drawing area.
project: Fix setting of restriction caps values
pipeline: Reimplement connectWithViewer for glimagesink
titleeditor: Fix the background color button

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=708411
titleeditor: Fix the background color button initialization
ui: Remove two unused methods
titleeditor: Simplify the UI

Stripped the buggy UI so that the text field shows only the text,
without colors etc. The font and color buttons now take effect on the
entire text, not only on the selection.

Removed the bold and italic buttons as these are specified by the font
chooser button.

Fixes:
https://bugzilla.gnome.org/show_bug.cgi?id=726473
https://bugzilla.gnome.org/show_bug.cgi?id=708412