[4.0] Enhance application device signal

[4.0] 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: Iaf10578871fb6283dcc18dd75402d9e605c171a4