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.
Thanks for backlogging.  As a note, we have been running into outdated license headers when we have tried to release the portlet projects (which reminds me I'll need to update my license file auto-generated by the IDE).  I was thinking the next time we do a uportal release we could run the license:format which replaces all the licenses with the new license.  However perhaps we should do it earlier rather than later just so we can have the same license header in our IDE whether working on portlets or uPortal.