Update Mongoose

[phosit]

We use Mongoose 3.1. Curently the newest Mongoose version is 7.9.

Version 3.1 does manage some background threads (were the event handlers are executed). Newer versions don't do that. We have to poll once in a while. That allows us to execute the event handlers in the task manager. We need repeating tasks (see #5874) to call poll once in a while.

[Langbart]

#4074 (27/Jun/16) is too similar, add additional comments as needed.