REVIEW: [NEXUS-6747] Replace usage of restlet RepositoryUrlBuilder

https://issues.sonatype.org/browse/NEXUS-6747

Calculate repository content urls based on BaseUrlHolder instead using restlet RepositoryUrlBuilder, without taking into consideration the "force base url" as that functionality will be dropped in the future (https://issues.sonatype.org/browse/NEXUS-6490 https://issues.sonatype.org/browse/NEXUS-6373)
BaseUrlHolder.get() should never return "" and the global settings should already be handled by the BaseUrlHolderFilter.

If that is not the case with Ext.Direct usage, we need to fix that... but otherwise, you should just BaseUrlHolder.get() and assume it has the proper value.