Enhance application device signal

Enhance application device signal

Currently, DALi developer cannot get any information about device events
like LanguageChangedSignal.

To make user can use these kind of signals fully,

1) Add Language / Region information getter api.
  - api         : GetLanguage() / GetRegion()

2) Add new signal type and new signal for Battery / Memory status.
  - signal type : LowBatterySignalType / LowMemorySignalType
  - signal      : LowBatterySignal / LowMemorySignalType
  - enum        : BatteryStatus / MemoryStatus

Change-Id: I86db387985d37013d44d9641aaca4848c00bdd2d
Signed-off-by: minho.sun <minho.sun@samsung.com>