Add "+ Update current snapshot" option, incl. menu

Updating the currently used snapshot involved quite a few steps as it is now, including manually using the Name autocomplete field to enter/select it. One problem with this is that the UI isn't actually telling which snapshot is currently in use.

Adding a "+ Replace current snapshot" option on the List tab would make this an easier process and cut down a few steps and at least one page load. Even speedier would be if it was also added to the menu (Admin menu) transforming it into a quick two step process - Select menu and then confirm the replace.