Bookmark form styles improvement

Closes #6004

Auditors: @bradleyrichter

Test Plan:

app/renderer/components/addEditBookmarkHanger.js

@@ -188,10 +188,10 @@ class AddEditBookmarkHanger extends ImmutableComponent {
             <div className='bookmarkButtons'>
               {
                 this.props.originalDetail
-                ? <Button l10nId='remove' className='removeButton whiteButton' onClick={this.onRemoveBookmark} />
+                ? <Button l10nId='remove' className='whiteButton wideButton' onClick={this.onRemoveBookmark} />
                 : null
               }
-              <Button l10nId='done' disabled={!this.bookmarkNameValid} className='doneButton primaryButton' onClick={this.onSave} />
+              <Button l10nId='done' disabled={!this.bookmarkNameValid} className='primaryButton wideButton' onClick={this.onSave} />
             </div>
           </div>
         </div>

less/forms.less

@@ -551,6 +551,7 @@
   background: linear-gradient(#FFFFFF, #DEDEDE);
   margin-top: 10px;
   padding: 0;
+  min-width: 310px;
 
   .arrowUp {
     width: 0;
@@ -572,15 +573,14 @@
   }
 
   .bookmarkButtons {
-    margin: 20px 0 10px 0;
-
-    .doneButton {
-      margin-right: 0;
-    }
+    display: flex;
+    justify-content: flex-end;
+    margin: 20px 0 10px;
   }
 
   .bookmarkFormInner {
     padding: 10px 30px;
+
     h2 {
       -webkit-user-select: none;
       cursor: default;

less/navigationBar.less

@@ -591,14 +591,6 @@
 }
 
 #navigator {
-  .bookmarkButtons {
-    display: flex;
-
-    .removeButton {
-      flex-grow: 1;
-    }
-  }
-
   .stopButton,
   .reloadButton,
   .homeButton {