Add manual way to refresh tags

Problem: on github in our project a new tag was created by somebody else. It was not yet present in tags list in sourcetree. I tried fetch on branches and other ways in SourceTree but wouldn't appear. Only by commandline with 'git fetch -t' and reopening project I would get them.

Suggestion: add a manual way to refresh tags by adding a refresh/fetch option in context menu below tags menu option.