GUACAMOLE-61: Add JDBC-specific tokens, including start date and time

[necouchman]

This is an attempt at resolving the challenge specified in the Jira ticket, which is that the default ${GAUC_DATE} and ${GUAC_TIME} tokens may not match up to the JDBC start date/time. JDBC-specific tokens have been added - including the start date/time, which are pulled from the ActiveConnectionRecord for the connection - which should allow the date and time to match up with the database records. Other tokens have been added, as well, which will also resolve some other Jira issues, such as wanting to use the connection name in the token.