es_ES: Added initial translations

PatchSet 2: Integrated changes of:
            http://review.cyanogenmod.com/#/c/25800/
            http://review.cyanogenmod.com/#/c/25825/
            Changed some strings for better appearance

PatchSet 3: Added some suggestions of Jorge Ruesga

PatchSet 4: Fixed "filesystem_info_dialog_tab_disk_usage"

Change-Id: Ib3d6b02a7b2aed121c425eac210de89a3b421732