cylc graph, cylc gui: add toolbar text, rename 'landscape' mode

If a user has their `toolbar_style` GNOME setting set to display text for toolbar items (via the `text` or `both` setting, but not applicable to the `both-horiz` one), text will appear beneath the icons on all GTK programs. Unfortunately, currently, quite a lot of the text that appears in the `cylc gui` and the `cylc graph` toolbars is then either missing (looks weird) or garbage (e.g. `Yes` appears as the text for `Ignore Cold Start Tasks` in `cylc graph`).

This change adds or changes toolitem label text where appropriate, so that `cylc gui` and `cylc graph` now look good with this toolbar style.

In GNOME 2, the setting can be altered by (GUI) loading up `gconf-editor` and navigating to `/desktop/gnome/interface/toolbar_style` or (CLI) running gconftool-2 for that path, and setting a value of `both` or `text`. 

In GNOME 3, the setting can be altered by running (GUI) `dconf-editor` or (CLI) `gsettings` with a similar path (e.g. see http://ubuntuforums.org/showthread.php?t=1501276).

I also renamed `Landscape Mode` to `Left-to-right` as, really, `Landscape` makes no sense - my bad :)

@hjoliver, please review.