Do not re-create SG::Animation when we call Clear to empty animation + Clear reset...

Do not re-create SG::Animation when we call Clear to empty animation + Clear reset some values

Since we always destroy & create scene obeject whenever we call Clear(),
It will be make some useless memory increasement when user call
Clear() infinitely.

To avoid this cases, let we re-create that object only if we call Play() before
or at least 1 animator exist.

And also, make Clear() API reset some sensitive values, like CurrentLoop and State.

Change-Id: I7f79b5e8e2bf822f01f094e4023e90e5f0922faa
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>