Improves New-MVPContribution

[PrzemyslawKlys]

This changes:

• Ability to define more than one AdditionalTechnology (as the interface allows this, so does API - not sure if more than 2 are allowed so for now I've not blocked anything)
• Improved speed of the cmdlet by caching types. Otherwise with each submits four GET queries would execute unnessecary
• Hopefully fixes New-MVPContribution returning 500 internal server error #19 as I was getting this error for some entries until I added UTF-8 in ContentType. Not sure if it's just luck that it started to work again or it really worked but no harm in doing so.
• Uses ConvertTo-Json from Hashtable rather than the string-based body. Easier to set things PowerShell way.

[lazywinadmin]

Thanks @PrzemyslawKlys ! Looks great! Thanks for your contributions! :)