Inline Filter#by_tag? and #by_tags?

* Use the collection methods #any? and #include? instead
Minor cleanups

* Didn't need a field for mappings
* consistency with local variable names in tag add/remove
Better comment for View::Mappings::Filter
Separate QS hash manipulation into own class
filter_by_type_path -> Filter::Query#by_type
remove_filter_by_type_path -> Filter::Query#remove_by_type
Move sort methods from helper

* To Filter::Query