pep8: fix new pep8 errors
project: check if values exist before setting caps
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.
gtk 3.14: use GtkBox instead of GtkVBox

Remove H and V from GtkBox, GtkScale, GtkPaned and GtkButtonBox
gtk 3.14: 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
gtk 3.14: 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
gtk 3.14: 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
gtk 3.14: remove various 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
gtk 3.14: overwrite all files with glade. Verify 3.12. Replace GtkTable with GtkGrid