Update libcynara-admin API header

Change const strings from const char* to defines.
Add missing struct keywords.
In function cynara_admin_set_policies() change polices parameter
to array of pointers.
In function cynara_admin_set_bucket() add extra parameter for
passing additional data to bucket's default policy.

Change-Id: Id1370a202a39636572aa6a203ae29662e423c986
Add stub implementation of libcynara-admin API functions

Prepare Logic and ApiInterface classes skeletons.
Remove old empty admin-api.cpp file.

Change-Id: I498e0e904dbd9dea3a07eaaa998a30fce21cb4e5