URBNG-35 Initial version of WebAPI: handling database

From now on all values are readed from database using play-slick plugin.
WebApi works on database/webapi.h2.db but it easy to change database.

Changes:
* values are readed from database
* all use cases of 'register', 'leave game' and 'join game' are examined,
like registering new user with existing login, joining game more than once
etc...
* added some simple tests