Add WorkersManager interface

Add WorkersManager interface

WorkersManager interface defines API for taking actions
triggered by matcher events on workers structures.

The mock implementation of interface is provided in matcher package.
It is generated using mockgen command:

mockgen	-package matcher \
	-destination=matcher/workersmanager_mock_test.go \
	-write_package_comment=false \
	git.tizen.org/tools/boruta/matcher WorkersManager

Change-Id: I026c661696b19a3443afc430e46d96abf9a272d5
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>