Support "javaType" for things that are not "type": "object"

[dflemstr]

There is nothing that says that only "type": "object" things can have "javaType". For example, I would want a Joda DateTime to be serialized as an integer (letting Jackson handle the actual conversion) but this is not possible to express right now.

[joelittlejohn]

Thanks David. This sounds like a perfectly reasonable change so lets include it in the next version.

[dflemstr]

How easy would this be to add? I would like to do it myself but I would have to spend some time figuring out what the contract of org.jsonschema2pojo.rules.Rule, which is not immediately obvious to me. If it's a small change then maybe it's better if somebody who is more familiar with the code base implements this.

[joelittlejohn]

I plan to release 0.4.5 tonight so I'm going to push this into 0.4.6.

[joelittlejohn]

I've generalised the implementation in #287 to allow for any schema type to be overridden using javaType (not just integers and numbers).