Replaced custom strings with Android defaults

PS2: also replaced menu_cut/copy/paste with strings from android.R.string

Change-Id: I7695b283faa66c6997fad372b31de2c678d222d0

Conflicts:
	packages/DocumentsUI/res/values-de/custom_strings.xml
	packages/DocumentsUI/res/values-es/custom_strings.xml
	packages/DocumentsUI/res/values-fr/custom_strings.xml
	packages/DocumentsUI/res/values-it/custom_strings.xml