Merge branch 'bugfix/VersionHistory-positioning' into develop

Fixed a bug in which the Version History menu was being hidden behind the Topic Information box. This had been introduced as part of a previous update to make the Topic Information box sticky (643d856).

Author: JeremyCaney

OnTopic.Editor.AspNetCore/Shared/Styles/Base/_callouts.scss

@@ -24,6 +24,7 @@
   &.topic-info {
     @extend                     .sticky-top;
     top                         : 136px+15px;
+    z-index                     : 10;
     border                      : 1px solid $grey-lighter;
     padding                     : 15px;
     width                       : 100%;