Start some nav and dropdown cleanup

* Remove border-radii on top of tab dropdown menus
* Remove the .dropdown and .dropup styles and instead place  on all
* Use  on dropdown carets intead of separately applying margin with a top alignment
* Some other misc cleanup

docs/assets/css/bootstrap.css

@@ -2693,13 +2693,7 @@ input[type="button"].btn-block {
   content: "\e160";
 }
 
-.dropup,
-.dropdown {
-  position: relative;
-}
-
-.dropdown-toggle:active,
-.open .dropdown-toggle {
+.open > a {
   outline: 0;
 }
 
@@ -2707,18 +2701,15 @@ input[type="button"].btn-block {
   display: inline-block;
   width: 0;
   height: 0;
-  vertical-align: top;
+  margin-top: 8px;
+  margin-left: 2px;
+  vertical-align: middle;
   border-top: 4px solid #000;
   border-right: 4px solid transparent;
   border-left: 4px solid transparent;
   content: "";
 }
 
-.dropdown .caret {
-  margin-top: 8px;
-  margin-left: 2px;
-}
-
 .dropdown-menu {
   position: absolute;
   top: 100%;
@@ -3140,6 +3131,7 @@ button.close {
 }
 
 .nav > li {
+  position: relative;
   display: block;
 }
 
@@ -3320,6 +3312,11 @@ button.close {
   display: block;
 }
 
+.nav-tabs .dropdown-menu {
+  border-top-right-radius: 0;
+  border-top-left-radius: 0;
+}
+
 /*
 // Prevent IE8 from misplacing imgs
 // See https://github.com/h5bp/html5-boilerplate/issues/984#issuecomment-3985989