Fix issue "pbkdf Authentication method not supported#20"

[Fiwel00]

Fixing issue pbkdf Authentication method not supported #20

refactoring under the hood of the request.js file which was using deprecated request-promise

adding partial support to FritzOS! 7.50

this pull request adds 2 bugs:

• tamdownload does not yield a file
• toggleswitch is not usable for FritzOS! 7.50, the implemation is not yet available

fritzDect.toggleSwitch = async (deviceId, value, options) => {
...
if (version >= 750) {
   //TODO when someone gets a smartswitch
   return { error: 'The implementation for FritzOS!7.50 is not available '}
}