Make the fields used in hashcode and equals generation configurable

[SpaceBison]

Added excludedFromEqualsAndHashCode option for specifying which properties should be excluded from equals() and hashCode() methods. It can be used both as an object-level array containing excluded property names or as a property-level boolean switch.

Example:

{
  "type": "object",
  "excludedFromEqualsAndHashCode" : [ "excludedByArray" ],
  "properties": {
    "notExcluded" : {
      "type" : "string"
    },
    "excludedByProperty" : {
      "type" : "string",
      "excludedFromEqualsAndHashCode" : true
    },
    "notExcludedByProperty" : {
      "type" : "string",
      "excludedFromEqualsAndHashCode" : false
    },
    "excludedByArray" : {
      "type" : "string"
    }
  }
}

notExcluded and notExcludedByProperty will be used while generating hashCode() and equals(), while excludedByProperty and excludedByArray won't.

I felt that excluding properties from the methods would be more fitting than listing the included ones (as discussed in issue #309), because that way the default behavior, which is including all properties in the methods, is modified rather than redefined.

[anuragpro]

Is this feature getting merged?

[SpaceBison]

Took me long enough, but I updated this PR at last. Not sure why do the oraclejdk7 Travis tests fail with message: The JAVA_HOME environment variable is not defined correctly. Might this somehow be my fault?

[SpaceBison]

Merged in 5eeb01e, now it builds. :)

[joelittlejohn]

Yeah. It looks like Travis changed their base image and broke installing of Oracle JDKs.