Fix wrong method name in release notes

I documented 'get_ancestors_and_itself', but the method is called
get_ancestors_and_self.
Small tweaks to comments

Conflicts:
	oscar/apps/search/handlers.py
Same signatures for product search handlers

As suggested in
https://github.com/tangentlabs/django-oscar/pull/1093#discussion_r16598106

this commit unifies the signatures for both handlers.
Rename modules from handlers to search_handlers

Handler is a very generic term, so this commit tries to use a more
specific name.
Methods to reason about Solr's presence and the search handler to use

Instead of hard-coding that logic in the view, it makes sense to have
dedicated methods for others to use.
Allow sorting by rating

To allow rating faceting to work, each product rating is rounded to the
nearest int so this sorting won't be as accurate as it could be. However
it's good enough for now.
Split out browsing all products from the category view

This makes the product category view much simpler and seems generally
cleaner.
Rework ProductCategoryView for readability

Since it's only a TemplateView, we can rename the internal methods to be
more readable. Should it be a DetailView though?

Conflicts:
	oscar/apps/catalogue/views.py
Use a separate template for category browsing

This avoids having logic in the template to switch between "all
products" and category browsing. It also allows some simplification in
the views.
s/AllProducts/Catalogue

Conflicts:
	oscar/apps/catalogue/views.py