Add common folder, add grid component, remove home placeholder

* New `common/` folder for `_variables` and `_global`
* Move grid styles to new `_grid` component
* Remove `layouts/pages/_home`

assets/styles/components/_grid.less

@@ -1,10 +1,10 @@
-// Content wrapper
+// Grid system
-.wrap { }
-
-// Main content area
 .main {
   .make-sm-column(@main-sm-columns);
   .sidebar-primary & {
     .make-sm-column(@main-sm-columns - @sidebar-sm-columns);
   }
 }
+.sidebar {
+  .make-sm-column(@sidebar-sm-columns);
+}

assets/styles/layouts/_sidebar.less

@@ -1,3 +0,0 @@
-.sidebar {
-  .make-sm-column(@sidebar-sm-columns);
-}

assets/styles/main.less

@@ -2,16 +2,15 @@
 @import "../../bower_components/bootstrap/less/bootstrap.less";
 // endbower
 
-@import "_variables";
+@import "common/_variables";
-@import "_global";
+@import "common/_global";
 @import "components/_buttons";
 @import "components/_comments";
 @import "components/_forms";
+@import "components/_grid";
 @import "components/_wp-classes";
-@import "layouts/_general";
 @import "layouts/_header";
 @import "layouts/_sidebar";
 @import "layouts/_footer";
 @import "layouts/_pages";
-@import "layouts/pages/_home";
 @import "layouts/_posts";