KH-189: Inform user of session timeout

Uses ng-idle to provide feedback about session timeout to customer.
Polls SessionResource on koodisto-service to keeps the session alive
while user appear active. Should handle adequately multitab sessions.
timeout is fetched from SessionResource dynamically, polling interval to
keep session alive is configurable and warning duration is hard coded to
5 minutes.
Merge branch 'develop' of https://github.com/Opetushallitus/koodisto into develop

Conflicts:
	koodisto-ui/src/test/java/fi/vm/sade/koodisto/config/ConfigControllerTest.java