Write MK-Task-like API

[bassosimone]

The goal is to run a Psiphon nettest using an API that is as close as possible to MK's Task API as it appears on Android and iOS. I have a prototype but it has not been committed.

[anadahz]

There is some precious conversation that may be proven useful in the future:
measurement-kit/measurement-kit#1425

[bassosimone]

@anadahz actually that issue is not much relevant, at this point. This issue is only about wrapping the already implemented in this repository Psiphon code so that it uses the MK Task API.