MAke HST configuration in memory model loading more efficient regarding cpu and memory usage

I think there are still a couple of areas we can gain performance improvement and memory improvements, namely:

CPU / startup improvements:

1) Only load the sitemap model after it is needed for matching OR when it is needed because the Mount it tried to be used for linkrewriting
2) Only load the locationtreemap for some sitemap once it is needed for linkrewriting and not at startup
3) Only enhance the HST component configuration for some hst:site when it is needed and not at startup

Memory improvements:

Clean up empty hashmaps and lists after the model has been build for things like the sitemap, locationtreemap and hst component configuration