Ensure that preference keys are not prefixed with '/' if ENV['RAILS_CACHE_KEY'] is not set

Fixes #3831
remove extra include for Search module in Spree::BaseController

Fixes #3852
[frontend] remove redundant via in routes

Fixes #3853
[api] Add assurances that line item prices cannot be set while creating or updating orders
centering search field on select2 plugin in admin area

Fixes #3854
Fixes #3842
Fix format of price input in products/new.html.erb
Use asset pipeline for jstree

Hard-coding links to /assets/ without fingerprints does not work on Rails 4
Remove version number from font awesome

The version number in the query string is not necessary for fingerprinted assets.

I'm not sure about the purpose of the #iefix anchor so I've left it in.

Additionally, some web servers do not handle query strings very well, such as SimpleHTTPServer.
[frontend] Stop people encountering uninitialized Taxon errors when they override ProductsController#show
Non-GET requests that would usually non-ssl-redirect will now respond with HTTP status 426

Conflicts:
	core/spec/lib/spree/core/controller_helpers/ssl_spec.rb