Adspace: modifications to exchange so that we support new wrapper settings

[dasgarner]

There are a number of new settings we should support:

• xiboPrefetch
• xiboValidType
• xiboValidDuration
• xiboMaxDuration
• xiboIsWrapperOpenImmediately
• xiboPartner
• xiboIsWrapperRateLimit
• xiboFileScheme
• xiboExtendUrl
• xiboHttpMethod

We also need to support LAT/LNG/LAT_START/LNG_START/UNIX_TIMESTAMP macros in the request/impression URLs.

This will bring the windows player up to date for various SSPs coming onboard in 3.3.0.

[dasgarner]

[ACTUAL_IMP] should be "" if not known.

[dasgarner]

If empty, this shouldn't be checked: https://github.com/dasgarner/xibo-dotnetclient/blob/develop/Adspace/ExchangeManager.cs#L740