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.
`EqualsBuilder` is a new import, so the preferred `lang3`.  `StringUtils` was an existing import, so left untouched.  

Certainly a judgment call, but there's something to be said for not changing the things one isn't touching.  Moving to lang3 more generally is backlogged as [UP-4270](https://issues.jasig.org/browse/UP-4270) and will presumably mop up that `StringUtils` import.