Minor fixes for some trees

* add missing + Object links
* specify list_view for Person, Document
* place {{#if viewLink}} and {{#if mappings}} correctly
Initialize widgets using JoinDescriptor specifications

* add GGRC.ListLoaders.ProxyListLoader
* remove Controllers.PageObject#init_related_widgets and friends
* add JoinDescriptor#get_list_loader
Don't show risk; don't use SystemControl
Change signature of Resource#get_properties_to_include

* preparing for eager-loading associations in ObjectView