Settings: fix storage measurement for device without emulated sdcard

StorageMeasurement: misc files should only be measured for internal
storage only if it is the emulated storage, otherwise misc count
for the primary storage will be erroneously duplicated on the
internal storage count.

StorageVolumePreferenceCategory:
  - Always create mMountTogglePreference to avoid null pointer
    exception for code that relies on it existing
  - Check if the keys exist before calculating totalValues to
    avoid null pointer exception on storage where media is not
    calculated
  - For available/readonly, set title, not summary (summary is
    supposed to be the amount available)

Change-Id: Ib217f79ee562dffc514696fff038e58ed0dba7d9
Settings: use DefaultContainerService for all file operations

For devices with non-emulated storage, the system uid is not allowed
to access the storage (to prevent system_server from being killed
on UMS mount). Old code remain that make file access directly, change
those to use DefaultContainerService

Depends on http://review.cyanogenmod.org/28179

Change-Id: Ie6bdaf27249daeabdc7f0ef1d73d484764ee35f0