Gallery2: Localize strings

Undo and redo were hardcoded in the photo editor. This allows their
localization.

Patch Set 2: Use new strings so that it may be better translated for
certain languages. (Translations in separate patch)

Change-Id: I63df977696b74128ca5e6fc45037b6b43d43a465
Gallery2: Filtershow toast translations

Toast translation strings that were copy-pasted from existing "undo" and
"redo" strings. Some of these may need to be modified for the toast to
fit on the screen.

Patch Set 2: Shorten Dutch strings as per Marco Brohet's suggestion.

Change-Id: Iaa42ca57dfdd327ffde35a77e320d7f04605f682