EventBus instead of AsyncTasks

I replaced AsyncTaks with EventBus ( :bus: ) that allows to achieve same results with 30% less code in library and 30% less code in the sample, and (for me at least) it is way more clear/easy to work.

I have also updated README file to describe EventBus - it is not ready to be merged (it was done for fork), so README file for sure needs to be changed, or use branch "bus" which does include old README file.

Please lets use that thread to discuss disadvantages of such solution, as I may be missing something. Also I do understand the point that such change is radical and will make all code not supporting newer versions of Teleport without some change.