Closes #25 for now.

ESP-IDF and ESP-ADF are provided as git submodules to the actual project
repository.

ESP-IDF's relevant commands (e.g. build, menuconfig) are provided using the
project's Makefile. Additionally, they are integrated into VSCode using
task.json and another addon to make commands available in the IDE's status
bar.

Instead, make use of the embedded ESP-IDF in ESP-ADF.

Basically this is just a matter of adjusting the paths in the Makefile,
so this is easy enough.

.vscode/c_cpp_properties.json is modified to reflect these paths.

The serial port to be used may be specified in the Makefile (ESP_SERIAL_PORT)
and is provided for this development machine.

Close #26

This commit includes several ugly and hackerish fixes.
Obviously, a HTTP stream requires actual access to the internet, but as of
now, map32 does not know if there is internet connectivity before it is
setting up the audio_source (http_stream in this case).

Obviously, map32 needs to know, if external peripheral devices (like
internet connection, but also SD reader, ...) are ready before using them
in its own codebase.

I.e. in the example code, there is a call to the function
``periph_wifi_wait_for_connected(wifi_handle, portMAX_DELAY);``, which
actually blocks until the WiFi is ready.

This needs a lot of investigation!