Run Liquibase migrations during application's startup time.

- new dependency was added: liquibase-core
- liquibase files was moved from src/main/config to src/main/resource to be available in classpath
- liquibase/full-changelog.xml file was renamed to liquibase/changelog.xml
- {h2,mysql}-scheme.sql: rolled back changes which will be performed by liquibase

No functional changes.