Connectors shouldn't try to manage the same thread pool

* app connectors use the server thread pool (null means inherit thread
  pool from server)
* admin connectors have their own shared thread pool that is now managed
  by the server instead of the individual connectors

Having multiple connectors manage the same thread pool was problematic.
To reproduce, run the example application and send a SIGTERM to the
process after it starts. It will timeout and give up stopping the admin
thread pool after 30 seconds instead of stopping cleanly right away.
Upgrade jetty-setuid-java to 1.0.2

Fixes #402
Add support for using Optional<DateTime> in dropwizard-jdbi

Add support for Optional<DateTime> in dropwizard-jdbi by handling NULL-values
in JodaDateTimeMapper. This also fixes a NPE-occuring when using the
existing mapper to plain DateTime-object if extracted column is NULL.
fix for bug in FileAppenderFactory where even if archive is set to true it returns a regulat file appender instead of rolling file appender
Avoid using reflection for testing a private method.

Instead, the method should probably at least be `protected`, which
allows us to override it in the test and make it testable.
Merge pull request #419 from klette/support-optional-datetime-in-jdbi

Add support for using Optional<DateTime> in dropwizard-jdbi
Merge pull request #416 from vadims/upgrade_jetty_setuid

Upgrade jetty-setuid-java to 1.0.2
Updated Liquibase to 3.0.7

Closes #411.
Merge pull request #415 from vadims/connector_threadpool

Connectors shouldn't try to manage the same thread pool