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.
Agree that wildcard imports are to be avoided and will be forbidden when we adopt Google Style.  That `import static org.junit.Assert.*;` is wrong in this respect.  (I bet IntelliJ auto-generated it when generating the unit test class.)  I'm not inclined to fix it in this changeset, since it will presumably be (trivially) mopped up when whatever module this ends up in adopts Google Style.