setting-keys: Add new vconf key to support multi-theme feedback

setting-keys: Add new vconf key to support multi-theme feedback

libfeedback has supported the only one feedback theme.
In order to support various theme of feedback, it requires
the new vconf key when changing the key on setting app.

So that add the following new vconf key for  multi-theme feedback as
- VCONFKEY_SETAPPL_ACCESSIBILITY_SOUND_FEEDBACK_THEME
  : libfeedback supports the sound feedback like power-on, power-off and
  beep sound. According to the value of theme selected by user,
  libfeedback plays the different sound for each feedback like power-on.
- VCONFKEY_SETAPPL_ACCESSIBILITY_VIBRATRION_FEEDBACK_THEME
  : libfeedback supports the vibration feedback like power-on, power-off and
  touch sound. According to the value of theme selected by user,
  libfeedback plays the different vibration for each feedback like power-on.

Change-Id: Ib85d6a92f7d44d2a3be631a3ec9d0b0d3a30d948
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>