Do not allow void_transaction! to take place if payment is already voided

Fixes sub-issue from #2119
[api] Always include a :payments key in payments response
[api] Fix ProductPropertiesController to use ID, rather than name

Fixes #2143
[api] Add capture endpoint for payments
[api] Don't use deprecated syntax in ProductPropertiesController
[api] whitespaces in ProductPropertiesController
Fix product properties API to not show properties for unavailable products
[api] Ensure there is always a :product_properties key returned by /products/:id/products_properties
[api] find by property id first, then name

This is to stop SQL errors like this from happening:

https://travis-ci.org/#!/spree/spree/jobs/2923604
[api] destroy statuses should return status 204
[api] allow build_from_api to accept empty line_item_attributes
Mark failing-on-travis tests as pending for now
Remove X-UA-Compatible from layout

Fixes #2152

Fixes #2151
[api] Tidy up parameters in zones_controller_spec
Fixing Jirafe Links, Fixes #2144

Fixes #2150
Remove ShippingMethod#calculator_available?

Related to #2149
Even more admin fixes!

* Replace static values with variables in admin stylesheets
* Remove unsude css reset file already. Now we use normalize.css on frontend and backend.
* Fix admin thead th font weight

Fixes #2146
Stripping EXIF from JPGs

Fixes #2142
Fixes #2145
Ensure ALL select2 choices show up in taxons for admin/products/edit

Fixes #2139
[api] Fix zones_controller_spec