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.
Jira vs. Github issues deserves continuing discussion on its own uportal-dev thread (I'm not entirely convinced it would be better).