Improve navbar toggle for mobile devices

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/generic/header.scss

@@ -76,15 +76,10 @@ header {
       }
 
       .navbar-toggle {
-        color: $style_color;
+        color: #666;
         margin: 0;
-        padding: 10px;
         border-radius: 0;
 
-        button i { font-size: 22px; }
-
-        &.collapsed { background-color: transparent !important;}
-
         &:hover {
           background-color: #EEE;
         }
@@ -106,8 +101,6 @@ header {
 
       .navbar-collapse {
         margin-top: 47px;
-        padding-right: 0;
-        padding-left: 0;
       }
 
       .navbar-nav {

app/assets/stylesheets/themes/gitlab-theme.scss

@@ -2,15 +2,12 @@
   header {
     &.navbar-gitlab {
       .navbar-inner {
-        .navbar-toggle {
-          color: #FFF;
-        }
+        .app_logo {
+          background-color: $color-darker;
 
-        .app_logo, .navbar-toggle {
           a {
             color: $color-light;
           }
-          background-color: $color-darker;
 
           &:hover {
             background-color: $color-dark;