UP-4330 MarketplaceEntry equals(), toString(), license header, and type JavaDoc.

 * Implements `equals()`, `hashCode()`, and `toString()` on `MarketplaceEntry` ( [UP-4330](https://issues.jasig.org/browse/UP-4330) ).
 * Adds Jasig license header.
 * Adds pro forma JavaDoc.
Great attention to detail @mmoayyed!  
(on soapbox)  I'd rather see insignificant items, especially trivial things like spaces or documentation improvements, cleaned up in commits without creating Jira issues including taking the opportunity to doing them in existing pull requests.  The Jira is getting cluttered with too much noise and it is becoming a less effective tool for managing and prioritizing work in part because of that.  Let's not create barriers to simple maintenance items that improve code health.  (off soapbox).