Update the folder structure for Enrollee implmentation.

Update the folder structure for Enrollee implmentation.

I have tried to make the relationship of folders be platform independent
and connectivity independent. And I have seperated the folders into Enrollee
and Mediator so that one can understand what the folder contains easily.

Additionally, I have changed the names of some functions to be expressed more clear.

Change-Id: I126d388178d473b56812fb597441ab4c481ec721
Signed-off-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1280
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
Tested-by: Uze Choi <uzchoi@samsung.com>