equals() and hashCode() methods are missing in classed provided by SDK

[kmichalak]

General information

• SDK/Library version: 2.27.2 and any previous version
• Environment: N/A
• Language, language version, and OS: Any version of Java and any OS

Issue description

Looks like equals() and hashCode() methods are not available for classes provided by SDK. It makes integration and unit testing much harder, as custom assertions/matchers are needed to check for example if com.braintreegateway.Trasanction instance contains all necessary data.
Currenlty to assert an object state I have to implement customer Hamcrest matcher, create long list of assertions (what is not the best idea from test design or good practices perspective) or use additional tools to perform reflection based comparison.
Adding implementation for equals() and hashCode() methods will simplify testing process.

[quinnjn]

I agree that it would be nice to have these methods implemented.

We'll keep this in mind as we try out lombok (mentioned in #57) which looks like it is able to generate equals and hashCode methods.

[hollabaq86]

for internal notekeeping, ticket 630