Invoke config changed callbacks directly

Invoke config changed callbacks directly

- Issue:
If the app changes the config using setting API, the framework did not
invoke config changed callbacks.

- Solution:
In previous code, tts_config_mgr module can knows the config changes by
checking the difference between the values in memory and config file.
However, the values in memory and config file were the same if the app
uses the setting API. This is because the setting API sets the value to
both memory and the file.
So, this patch adds a new logic for invoking the callacks. Through this
patch, tts_config_mgr module calls the related callbacks in case the app
changes the config itself.

Change-Id: If2da13a32e8e12b321812586e4c4bb93fd5f769e
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>