Wicket 1.5.1 released

This is the first maintenance release of the Wicket 1.5.x series. This release brings over 40 bug fixes and 15 improvements.

<dependency>
    <groupId>org.apache.wicket</groupId>
    <artifactId>wicket-core</artifactId>
    <version>1.5.1</version>
</dependency>