introduce OathList class

- move non-final static members and static methods of OathObject to
  OathList, so they can't be read/set by other applets
- change OathObject creation to require list as parameter
- remove asserts from test that worked on leaking state
configure travis to skip install phase

- replace pre_install with install so it won't run gradle install phase

simplyfy trafi
Merge pull request #3 from fidesmo/fix-internal-state-leakage

introduce OathList class