Add basic AP support

[bjoernQ]

This adds support for creating an open access-point
Closes #60

This will enable us to implement WiFi provisioning via an open AP. Doing that in a convenient way will need a few more things which don't belong here - I plan to create a demo / example for that outside of this repository.

• trying to create a non-open AP currently triggers an exception in the WiFi driver
  • in hostapd_setup_wpa_psk
  • calling ROM function multi_heap_malloc_impl
• not sure if is_connected should do anything useful in AP mode - currently it doesn't
• there are quite a lot of places now where we need to differentiate between the modes
  • not sure how we can make that nicer, I also would prefer to improve that in a separate PR to keep this initial PR small

If we want to support APSTA (AP and STA at the same time) we need a larger refactoring - plus APSTA currently triggers an exception in the wifi driver. Investigating this might be a lot of effort and something for another day.

[MabezDev]

Overall LGTM! Both examples work well for me. Just a couple if comments to address.