Update ESAPI pom to use latest version of AntiSamy (1.7.6) #847

A new version (1.7.6) of AntiSamy was just released. Update pom to use it and update other dependencies and plugins to latest compatible version as well.

Note since there were no vulnerabilities addressed in AntiSamy and this change is unlikely to affect ESAPI users, I'm considering this an enhancement rather than a bug.