Compile scss with Compass

- Replace Sass by Compass
- Replace grunt-sass by grunt-contrib-compass plugin
- Fix errors pointed by Compass
- This is being introduced to be able to efectivelly compute color
  contrast. Compass has 
  http://compass-style.org/reference/compass/utilities/color/contrast/
  and any other implementation needs pow() with decimal numbers, also
  provided by Compass.

Gruntfile.js

@@ -134,14 +134,12 @@ module.exports = function(grunt) {
             },
             all: ['app/scripts/**/*.js']
         },
-        sass: {
-            options: {
-                sourceMap: false,
-                includePaths: ['./bower_components']
-            },
+        compass: {
             dist: {
-                files: {
-                    'tmp/css/main.css': 'app/styles/main.scss'
+                options: {
+                    sassDir: 'app/styles',
+                    cssDir: 'tmp/css',
+                    importPath: ['./bower_components']
                 }
             }
         },
@@ -290,7 +288,7 @@ module.exports = function(grunt) {
             },
             styles: {
                 files: 'app/styles/**/*.scss',
-                tasks: ['sass']
+                tasks: ['compass']
             },
             indexhtml: {
                 files: 'app/index.html',
@@ -451,7 +449,7 @@ module.exports = function(grunt) {
         'copy:fonts',
         'webpack',
         'uglify',
-        'sass',
+        'compass',
         'postcss',
         'inline',
         'htmlmin',

app/styles/base/_forms.scss

@@ -182,7 +182,7 @@ input[type=checkbox] {
 
 $thumb-size: 14px;
 
-&input[type=range] {
+input[type=range] {
   -webkit-appearance: none;
   width: 100%;
   margin: 12px 0;

app/styles/common/_icon-select.scss

@@ -1,4 +1,4 @@
-&.icon-select {
+.icon-select {
   &__items {
     @include display(flex);
     @include align-items(flex-start);

app/styles/main.scss

@@ -1,4 +1,4 @@
-@import "../bower_components/normalize.css/normalize";
+@import "../bower_components/normalize.css/normalize.css";
 @import "../bower_components/font-awesome/scss/font-awesome";
 @import "../bower_components/pikaday/scss/pikaday";
 @import "../bower_components/bourbon/app/assets/stylesheets/bourbon";

package.json

@@ -19,6 +19,7 @@
     "grunt": "1.0.1",
     "grunt-bower-install-simple": "1.2.3",
     "grunt-contrib-clean": "1.0.0",
+    "grunt-contrib-compass": "1.1.1",
     "grunt-contrib-compress": "1.3.0",
     "grunt-contrib-copy": "1.0.0",
     "grunt-contrib-deb": "github:keeweb/grunt-contrib-deb#ddb2ef4",
@@ -30,7 +31,6 @@
     "grunt-gitinfo": "0.1.8",
     "grunt-inline-alt": "0.3.10",
     "grunt-postcss": "0.8.0",
-    "grunt-sass": "1.2.0",
     "grunt-string-replace": "1.2.1",
     "grunt-webpack": "1.0.11",
     "handlebars": "4.0.5",