Add transactions support

[serge-rider]

We have to im[plement #6 first

[StefanOltmann]

I see, that's why it won't work with JetBrains Exposed.

java.sql.SQLFeatureNotSupportedException: null
	at com.dbeaver.jdbc.model.AbstractJdbcConnection.setTransactionIsolation(AbstractJdbcConnection.java:131)
	at org.jetbrains.exposed.v1.jdbc.statements.jdbc.JdbcConnectionImpl.setTransactionIsolation(JdbcConnectionImpl.kt:85)