core: Separate main logic to storaged_init/exit function for common usage

core: Separate main logic to storaged_init/exit function for common usage

To make the init/exit sequences of the main function can be used by
other source files such as plugin library, the init/exit logics are
separated as 'storaged_init' and 'storaged_exit' respectively.
Accordingly, main.c file which includes main function is renamed to
storaged.c.

Also, to make them callable, header storaged.h is added.

Change-Id: I7f5512ae13a84095e94b9d56f9970ce09b1f9f0b
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>