update(demo, gridlist): add breakpoints for -xs

Author: ThomasBurleson

src/components/gridList/demoBasicUsage/index.html

@@ -1,6 +1,6 @@
 <div ng-controller="AppCtrl as appCtrl" ng-cloak>
   <md-grid-list
-        md-cols-sm="1" md-cols-md="2" md-cols-gt-md="6"
+        md-cols-xs="1" md-cols-sm="2" md-cols-md="4" md-cols-gt-md="6"
         md-row-height-gt-md="1:1" md-row-height="2:2"
         md-gutter="12px" md-gutter-gt-sm="8px" >
 

src/components/gridList/demoDynamicTiles/index.html

@@ -1,6 +1,6 @@
 <div ng-controller="gridListDemoCtrl as vm" flex ng-cloak>
   <md-grid-list
-        md-cols-sm="1" md-cols-md="2" md-cols-gt-md="6"
+        md-cols="1" md-cols-sm="2" md-cols-md="3" md-cols-gt-md="6"
         md-row-height-gt-md="1:1" md-row-height="4:3"
         md-gutter="8px" md-gutter-gt-sm="4px" >
 

src/components/gridList/demoResponsiveUsage/index.html

@@ -1,9 +1,9 @@
 <div ng-controller="AppCtrl as appCtrl" ng-cloak>
   <md-content layout-padding>
     <md-grid-list
-        md-cols-gt-md="12" md-cols-sm="3" md-cols-md="8"
+        md-cols-gt-md="12" md-cols="3" md-cols-md="8"
         md-row-height-gt-md="1:1" md-row-height="4:3"
-        md-gutter-gt-md="16px" md-gutter-gt-sm="8px" md-gutter="4px">
+        md-gutter-gt-md="16px" md-gutter-md="8px" md-gutter="4px">
       <md-grid-tile
           ng-repeat="tile in appCtrl.colorTiles"
           ng-style="{