Enable SCSSLint

See https://github.com/silverstripe/silverstripe-asset-admin/pull/129
and https://github.com/silverstripe/silverstripe-asset-admin/pull/130 for context

.codeclimate.yml

@@ -1,6 +1,8 @@
 engines:
   eslint:
     enabled: true
+  scss-lint:
+    enabled: true
   duplication:
     enabled: true
     config:

.scss-lint.yml

@@ -0,0 +1,61 @@
+# See https://docs.silverstripe.org/en/4.0/getting_started/css_coding_conventions/
+# Install instructions: https://github.com/brigade/scss-lint
+# Adapted from https://github.com/airbnb/css
+# Used for CodeClimate CI checks.
+
+scss_files: '**/client/src/**/*.scss'
+
+exclude:
+  - 'client/src/styles/legacy/*'
+  - 'admin/client/src/styles/legacy/*'
+
+severity: error
+
+linters:
+
+  BorderZero:
+    enabled: true
+    convention: zero
+
+  BemDepth:
+    enabled: true
+
+  DeclarationOrder:
+    enabled: false
+
+  ExtendDirective:
+    enabled: true
+
+  LeadingZero:
+    enabled: false
+
+  NameFormat:
+    enabled: true
+
+  PrivateNamingConvention:
+    enabled: true
+    prefix: _
+
+  PropertySortOrder:
+    enabled: false
+
+  QualifyingElement:
+    enabled: false
+
+  SelectorFormat:
+    enabled: true
+    convention: hyphenated_BEM
+    class_convention: ^(?!js-).*
+    class_convention_explanation: should not be written in the form js-*
+
+  SingleLinePerProperty:
+    enabled: true
+    allow_single_line_rule_sets: false
+
+  StringQuotes:
+    enabled: true
+    style: double_quotes
+
+  UrlQuotes:
+    # TODO Re-enable once it support double quotes
+    enabled: false