Added toString, hashcode, and equal methods

[cammace]

This PR adds the standard toString hashcode and equal methods to model classes. Previously, if you tried comparing two matching objects, it would return false, this fixes that.

• Test should be added
• Javadoc needs to be added

[zugaldia]

@cammace I like the idea of adding these methods, but as the models and API support grow, this process is manual, tedious, and error-prone.

I'd like to propose an alternative approach to automate this process. My current thinking is to use auto-value-gson to generate all the model classes. This comes with the following benefits out of the box:

• Gson support.
• Creation of equals, hashCode, and toString automatically for all models.
• Possibility to attach a builder to each method to address Make model constructors more consistent #441

This is a larger change and before we do it I'd like to hear 👍/👎 from @mapbox/android.

[cammace]

I'd like to propose an alternative approach to automate this process

My original hesitation for doing this was the overhead that comes with maintaining all these methods. Any means to automate this process sounds great to me.

[cammace]

Since AutoValue will require a bunch of API breaking changes we are holding off till 3.0.0 gets released (discussed in #499). Moving forward with this PR in the meantime. Can I get your review again @zugaldia

[zugaldia]

Were all tests and Javadoc added to the PR, or is this still pending as per OP?

[cammace]

I chose not to include test and Javadoc since we plan to switch to AutoValues very soon (which won't require us to test this).

[cammace]

If you agree that we don't need to add test/javadoc for this, could I get another round of reviews?

[cammace]

Removing from the 2.2.0 milestone since this isn't an immediate feature needed and most likely the 3.0 release will bring AutoValues which handles this for us.

[Guardiola31337]

Noting here that when using Kotlin Data Classes the compiler automatically derives equals()/hashCode() and toString() providing everything you need to make AutoValue (in most cases) not necessary (avoiding a 3rd party dependency).

[cammace]

AutoValue works coming in 3.0.0 release which resolves all the things mentioned in this PR, closing.