Allow alternative data collection systems to integrate with queXS (i.e. not Limesurvey)

queXS is intimately linked with Limesurvey. It includes a customised version of Limesurvey that allows for many useful features to be intergated with the calling system (such as queXS sample -> Limesurvey tokens, quotas, etc). There are cases where queXS is required only for call and sample management, and not for data input (such as when using an existing online questionnaire for data input). queXS should support this method by allowing a questionnaire to be created and either not linking it to a data input system at all, or linking it via an external URL and with the ability to pass a token or set of values via a GET or POST request, which would allow the data input window to appear where Limesurvey currently appears. It should be tested first with an external Limesurvey installation, and then with other customised systems.