res: Move shutdown menu array items to strings

for easier translation work on the overlays added by
http://review.cyanogenmod.com/8471

String 'Bootmenu' (and its de translation found from the patch) is added.

patch set 2: String 'Fastboot' is added as requested.

This patch is needed by http://review.cyanogenmod.com/8631

Change-Id: I1f89f2670facec9a60d1b2981bd71f705f887f04