Split package caused by DisableStrictChecks

Hello, Tapestry developers,

The @DisableStrictChecks annotation 
(https://issues.apache.org/jira/browse/TAP5-2655) causes a split package 
(in terms of Java 9 modules) with tapestry-core.

In my opinion, the best fix is to move it into tapestry-core. While the 
jar would change, the package would stay the same, causing fewer to no 
migration issues - hopefully.

Keeping it in tapestry5-annotations would imply moving it to another 
package, definitely causing some sort of migration efforts.

Keen to hear your thoughts.

Thanks,

Volker