Implement API for managing list of permitted labels for launcher

Implement API for managing list of permitted labels for launcher

Four new API functions:
- security_manager_app_labels_monitor_init
- security_manager_app_labels_monitor_finish
- security_manager_app_labels_monitor_get_fd
- security_manager_app_labels_monitor_process

They provide functionality needed for the launcher to run without
CAP_MAC_ADMIN. It will rely on new feature of Smack:
relabel-self list of labels, that a process can change its label
to without special capabilities.
The new APIs will enable the launcher to wait for changes of
apps labels list (when an app is installed or uninstalled) and
to update its relabel-list with a separate, dedicated function.

Change-Id: I1d8a7bce8c081ba27e7c388ee096c7c07005d92d
Signed-off-by: Radoslaw Bartosiak <r.bartosiak@samsung.com>