setting-keys: Add VCONFKEY_SETAPPL_TIMEOUT_DIM

setting-keys: Add VCONFKEY_SETAPPL_TIMEOUT_DIM

It takes time in second, and if the value is nonnegative, it fixes
screen dim timeout by the value.

 - If the value is negative, then the screen dim timeout works same as
   before, 30% of VCONFKEY_SETAPPL_LCD_TIMEOUT_NORMAL.

 - If the value is nonnegative, dim state consumes its own timeout,
   VCONFKEY_SETAPPL_TIMEOUT_DIM. By this, normal state solely consumes
   entire VCONFKEY_SETAPPL_TIMEOUT_NORMAL, not sharing it with dim.

Change-Id: Ica90eb742f149ac8b3bf3f9c6894f0ff8f376e78
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>