Use unix timestamps in queries.

Fixes #339 ( #312 #328 ) by using FROM_UNIXTIME in the query even if using the paramaterised version, as java timestamps are not timezone-aware.  Also fixed the same thing in the chat insert.

My current minecraft test server timezone is UTC+1 (UK summer time).  I set my test MySQL server to UTC+2 and did the following tests.

Before change:
![2013-06-07_15 56 22](https://f.cloud.github.com/assets/426814/624553/0fb20e4e-cf88-11e2-8e22-6d8ccf141e37.png)

After change:
![2013-06-07_16 22 08](https://f.cloud.github.com/assets/426814/624555/1dc8117c-cf88-11e2-8e91-4a4e165a477e.png)

(times mentioned in chat are from the minecraft server's perspective)