chore(engine): use script task listener from deployment

related to #CAM-2361
feat(engine): add script as possible sequence flow condition

related to #CAM-2359
refactor(UI-TEST): implement page objects

This commit refactors the webapp UI test suite for page object
introduction.
test(UI-TEST/admin): add groups page tests
test(UI-TEST/admin): add admin user setup test
refactor(UI-TEST/admin):improve object instatiation

introduced index.js files for each group of page objects
test(UI-TEST/admin): add Authorizations test