Assets: create accounts with password auth and hashes

The password is: testtest
JPA: don't erase schema on startup
ConferenceService: distinct was missing in select
Tests: purge test data before test

Each test leaves the db populated after tests and purges the db before each individual test.

This means that after running the tests, you will still have some test data in the db if you want some for running the application.
Test: fix bug that caused failing testCreate()
Merge pull request #34 from stoewer/master

Tests: improved tests and test assets

LGTM