[DOC] Improve tree view colors attribute description

Add example for tree view colors attribute. Add note about escaping < and >. 
Add "(Tree views)" to the header additionally, as in other places in documentation, <tree> is still called  "Tree view"
Add link to the reference of the tree view from the backend tutorial
Neither am I. However it's better then the current situation, where in different part of documentation we use Lists and in other "Tree view" and it's really confusing for the newcomers, to get that list==tree.
What is your suggestion to improve the status quo?