SystemUI: Simplified Chinese Translations

Patch Set 2: Rearranged strings as per Marco's suggestions.

Patch Set 3: Added translations for the volume toggle in QuickSettings.

Patch Set 4: Fixed whitespaces.

Patch Set 5: Rearrangement of strings again.

Change-Id: I91de1d7d4d9adc0b97761b68799d624ee5da418b