Added phpdoc on all getters

This simplifies the usage of the SDK by allowing IDEs to provide autocompletion rather than having unknown types everywhere.

I also added the array initialization of array properties, to ensure that they are always arrays even if the serializer does not set them for some reason (the incomplete Analysis returned in ``getAnalysisStatus`` for instance).
Hm, actually, the type is "int" our database. then in the [XML](https://github.com/sensiolabs/insight/blob/master/Sdk/Tests/fixtures/project.xml#L1560), it could be interpreted as int.

I opened a PR to fix that: https://github.com/sensiolabs/insight/pull/36