Issue title: Feature Request: UI element indicating version
 Issue body: Not really a issue more of a Feature Request

Would be a nice little addition to have somewhere in the browser home page, or perhaps settings, the current version that is running. 
Ideally it would also include another UI element that indicates the status of if they are actually running the latest available verion or not, this would help users stay as up to date as possible with out requiring they monitor slack or github for new version announcements. 

Ty
 Comments: 
 Comment 0: @larrysalibra @yknl It would be nice to add an initial splash screen upon startup of the Blockstack Browser.
 Comment 1: I'd like to see this too!
{'source': 'GithubIssues', 'repo_name_with_owner': 'blockstack/blockstack-browser', 'issue_id': 283989704, 'repo_stars': 1131.0}