UP-4330 MarketplaceEntry nicities

 * Implements `equals()`, `hashCode()`, and `toString()` on `MarketplaceEntry` ( [UP-4330](https://issues.jasig.org/browse/UP-4330) ).
 * Adds Jasig license header.
 * Adds pro forma JavaDoc.
We had discussed adopting Google Code standards, one of which is no wildcard imports.  https://google-styleguide.googlecode.com/svn/trunk/javaguide.html#s3.3.1-wildcard-imports.  I know I have altered my intelliJ configuration to not import * unless there are 15 or 20 imports.