Added unique id to display devices and their settings.

The display setting saved to disk were using a localized name for
the key. This is an issue if the user changes languages after the
display settings have been saved. We now use the non-localized
name for the display to access the settings if it is available,
else we fall back on the localized name.

Bug: 18190800
Change-Id: I837c06a8935df10727229a1aa2bb6eeb3953707f