m-config-static-nodes: remove unneeded 'conected' callback and create static nodes when the plugin is activated

+ rename FEATURE_CONTROLS to FEATURE_PROPS
+ add accessor for the standard spa_param_info (info->params)
+ hide the low-level params API that nobody uses

The extra `../` only works if the build directory is an immediate child of the
source directory. In all the other configurations this breaks the build.

Dropping the extra `../` makes use of the `-I${SOURCE_DIR}` provided by meson.

Signed-off-by: Eric Engestrom <eric@engestrom.ch>

It can be a bit tricky because the "installed" signal may be fired
from inside the context of wp_core_install_object_manager(),
in which case the main loop should not be executed (or it will never quit)

We can now call wp_proxy_request_destroy() on endpoint links and
the WpImplEndpointLink together with the session item that created
it will be cleaned up

+ better logs by default
+ allow loading modules in tests

+ enable the new log writer on the executables
+ enable structured logging in the tests