mostly docs updates, but also some bug fixes per github issues

lib/forms.less

@@ -93,10 +93,14 @@ input[type=file] {
   line-height: @baseLineHeight * 1.5;
 }
 
+// Chrome on Linux needs background color
+select {
+  background-color: @white;
+}
+
 // Make multiple select elements height not fixed
 select[multiple] {
   height: inherit;
-  background-color: @white; // Fixes Chromium bug?
 }
 
 // Remove shadow from image inputs

lib/media-grids.less

@@ -1,26 +1,33 @@
-// MEDIA GRIDS
-// -----------
+// THUMBNAILS
+// ----------
 
-.media-grid {
+.thumbnails {
   margin-left: -20px;
   margin-bottom: 0;
+  list-style: none;
   .clearfix();
-  li {
-    display: inline;
-  }
-  a {
-    float: left;
-    padding: 4px;
-    margin: 0 0 20px 20px;
-    border: 1px solid #ddd;
-    .border-radius(4px);
-    .box-shadow(0 1px 1px rgba(0,0,0,.075));
-    img {
-      display: block;
-    }
-    &:hover {
-      border-color: @linkColor;
-      .box-shadow(0 1px 4px rgba(0,105,214,.25));
-    }
-  }
+}
+.thumbnails > li {
+  float: left;
+  margin: 0 0 20px 20px;
+}
+.thumbnail {
+  display: block;
+  line-height: 1;
+  border: 1px solid #ddd;
+  .border-radius(4px);
+  .box-shadow(0 1px 1px rgba(0,0,0,.075));
+}
+// Add a hover state for linked versions only
+a.thumbnail:hover {
+  border-color: @linkColor;
+  .box-shadow(0 1px 4px rgba(0,105,214,.25));
+}
+// Images and captions
+.thumbnail > img {
+  display: block;
+  margin: 4px;
+}
+.thumbnail .caption {
+  padding: 9px;
 }