Convert all request in the hmi javascript to async

[HolgerJeromin]

The browsers are moving away from support of sync requests. Right now they throw a warning only.

Solution 1:
Converting the requests to async is a huge task (callback hell) . But new language additions make this easier.
Old browsers allow sync requests, browsers in the future will provide modern stuff to be able to handle the situation. This issue should develop ideas for solutions:

http://chrisbuttery.com/articles/synchronous-asynchronous-javascript-with-es6-generators/

Implementing this new stuff probably allows to throw away the current complicated observer code.

Solution 2:
Most/some/all sync calles were done to prevent loosing a variable. Perhaps using the pattern IIFE will result in working async calls.