Remote control for phyphox

[jer194]

The existing API is already great to get data from a mobile device at remote locations!

I'm missing a few features though:

General:

- Configurable port for the web interface (see request on github).
- General setting for having the web interface always enabled;
    currently it is only possible when an experiment has been selected already.
    About security: no concerns as long as the web interface is not exposed to the public internet 

Web interface and/or API:

- Option to reset data
- Option to switch experiments
- Option to configure new experiments

Thanks!
Jakob.