* updated checkin entity

* updated checkin entity

* satisfying tests, detekt, ktlint, circle-ci, ...

* satisfying instrumented tests

* fixed more unit tests, removed unnecessary null-check

* renamed field

* made signature base 64

* fixed tests

* fixed signature tests

* ktlint

* no more use of blob

* updated repository

* fixed unit tests

* fixed instrumented tests

* renamed tests

* fixed merge conflicts