XHR method, exclude fields from secondary payload, polyfills

[flesheatingarthropods]

• I added an xhr method to the transports method (needs more work)
• I added a way to exlude fields from the payload for the secondary tracking call
• Since this uses stuff not available in older browsers (Object.keys, array.map, array.indexOf, foreach) I included the respective polyfills
• I reorganized the code a bit to avoid one giant "god function"

Changes might be a bit too extensive, when in doubt you can always pick and choose :-)