allowing to filter query by json objects

[dpoetzsch]

We have a live query on a pointer-typed column.

To make it work on Android we added an overloaded version of your where method that takes JSONObjects so we are very flexible to build our queries.

This is not ideal, because we have to build the JSONObject by hand as Parse on Android, different from JavaScript, does not allow to call toJSON on a ParseObject. Still, it provides enough flexibility to allow people to write all queries they are interested in, not only queries filtering on String-typed columns.