Make Actor's name don't use ConstString

Make Actor's name don't use ConstString

Since ConstString register into internal string pool
and never be released,
Their might be occured some memory limits if user use randomized name.

Until now, we use raw string comparision at FindChildByName.
So their is no performance issue after this patch.

TODO : How could we resolve same issue for RegisterProperty?

Change-Id: Ia4258d204e986c117f19489a075e3c5afff9fab9
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>