Convert tests to use MiniTest
"expected" argument comes first on assert_equal

Also convert a few instances of just assert foo==bar to use
assert_equal so a better error message is generated
Setup routes testing controller under Rails 4
Supply "importer" argument for CssParser >= 3.4

When Sass implemented source map support in version 3.4,
the signature of Sass::SCSS::CssParser.new changed to require
3 arguments