Do not show about dialog in menu and .desktop when installed via store?

[JMoerman]

Similar to #42, if installed via a store like AppCenter this information can be seen in the store.

Some issues with this:

• Can only show one author
• No way to credit artists

This information could be shown elsewhere like on the project homepage, but that requires people to put some effort in finding this information.

[cassidyjames]

If you wanted, you could add additional credits to the description if you think it is or should be of interest to current or potential users. But typically this information does make sense to go on the project's home page.

[JMoerman]

I think I'll just get it added to the project page. 1.6.3 won't show these dialogs on elementary OS.