clean up modals.less comments, add new class for optional use on modal forms to remove bottom margin

docs/assets/css/bootstrap.css

@@ -2888,6 +2888,9 @@ button.btn.small, input[type="submit"].btn.small {
 .modal-body {
   padding: 15px;
 }
+.modal-body .modal-form {
+  margin-bottom: 0;
+}
 .modal-footer {
   padding: 14px 15px 15px;
   margin-bottom: 0;

less/modals.less

@@ -1,6 +1,7 @@
 // MODALS
 // ------
 
+// Recalculate z-index where appropriate
 .modal-open {
   .dropdown-menu {  z-index: @zindexDropdown + @zindexModal; }
   .dropdown.open { *z-index: @zindexDropdown + @zindexModal; }
@@ -8,6 +9,7 @@
   .tooltip       {  z-index: @zindexTooltip  + @zindexModal; }
 }
 
+// Background
 .modal-backdrop {
   position: fixed;
   top: 0;
@@ -25,6 +27,7 @@
   .opacity(80);
 }
 
+// Base modal
 .modal {
   position: fixed;
   top: 50%;
@@ -53,9 +56,17 @@
   // Close icon
   .close { margin-top: 2px; }
 }
+
+// Body (where all modal content resises)
 .modal-body {
   padding: 15px;
 }
+// Remove bottom margin if need be
+.modal-body .modal-form {
+  margin-bottom: 0;
+}
+
+// Footer (for actions)
 .modal-footer {
   padding: 14px 15px 15px;
   margin-bottom: 0;