REVIEW: [NEXUS-5651] Siesta resources authorisation

https://issues.sonatype.org/browse/NEXUS-5651
https://bamboo.zion.sonatype.com/browse/NXO-OSSF49

The fix will solve two issues:
1. Make browsers pop up the basic auth dialog in case that user is not authenticated
2. Make possible to access siesta resources via rest clients as wget/restclient/curl

The fix does not solve the issues related to accessing siesta resources when security is off. 

The fix requires that siesta resources (/service/siesta/**) to be filtered through Shiro "authBasic" filter. The pull request introduces a generic way to configure Shiro filter chains.