CandidateSelectionTest testsuite

[rkrenn]

this is the intial commit for our End-To-End test based on chrome webdriver/selenium server. it is to be executed automatically by the GitHub java CI (see "Actions" https://github.com/phoenixctms/ctsms/actions).

the first use case covered now is the "Subject Candidate Selection", as raised by AGES Inspektion KPAM 398.

#todo