find method to look up object by primary key

[astigsen]

Right now to look up a single object by primary key, you have to make a full query and then do a findFirst().

It would be nice if you could do a direct lookup with a method like:

MyObject obj = realm.find(MyObject.class, objId);

(the Swift, C# and Javascript bindings all have methods like this)

[cmelchior]

This was already partly tracked here: #2166, just called get(). We should probably use the same name as the other bindings though.