Added spec to prove user_plugins failure to update, per #2580
Issue #2580

Changed user_params to permit an array of plugins. Without this, user plugin access was not being persisted.
Remove httparty from test from 3277e67e8afb039500683f414b2df98e5e176fe9

This closes #2555
This closes #2552
Hybrid positive/negative assertion to prove image's presence
Merge branch 'master' of github.com:refinery/refinerycms
Vertical admin tabs

Having admin tabs at the top running horizontally means they have to fit into a finite space. If there are too many, they go into a carousel, which is very inconvenient for navigation, and makes the rightmost tabs invisible to users.

I've put the admin tabs vertically at the left of the admin area. This gives as much vertical space (with scrolling) as needed.

- positioned admin tabs vertically at left
- wrapped admin content in #admin_container div
- corresponding #login_container div for login page
- more rounded corner mixins
- box-sizing mixin
- admin_background mixing provides faux column gradient background for admin area (modern browsers and IE10 up)
- SASS variables for $menu_width and $standard_rounding
- sortable_menu.js setting changed to y axis
- removed jcarousel and images
- replaced arrow_switch.png with arrow_up_down.png and arrow_left_right.png
- moved SASS utility mixins to a separate file
- generalised admin_background() mixin to faux_columns_2()
- removed different padding/margin for active tab
Merge branch 'admin_tabs_redesign' of github.com:isaacfreeman/refinerycms into admin_tabs_redesign