Added audiovisual emotion learner (develop) (#251)

* added av emotion learner

* added demo

* updated index.md

* fixed licenses

* pep8 fixes

* pep8 fix

* dependencies fix

* delete redundant files from demos

* Update tests/sources/tools/perception/multimodal_human_centric/audiovisual_emotion_recognition/test_audiovisual_emotion_learner.py

Co-authored-by: ad-daniel <44834743+ad-daniel@users.noreply.github.com>

* demo fix

* simplify imports

* pep8 fix

* pep8 fix

* Fix sources

Co-authored-by: ad-daniel <44834743+ad-daniel@users.noreply.github.com>
Co-authored-by: ad-daniel <daniel.dias@epfl.ch>