feat(#128): Fix requirements and paths (#129)

# Description

It was not possible to train a new model because some dependencies where
missing and the required package was not added to PATH.

Did some research, what's the best way to add some custom packages to
PATH.

Fixes #128 

## Time invested

Tim Dreier: 45 min

## Type of change

Please delete options that are not relevant.

- Bug fix (non-breaking change which fixes an issue)

## Does this PR introduce a breaking change?

No.

## Most important changes

```
$ b5 shell
$ cd /workspace/code/perception/src/traffic_light_detection
$ python src/traffic_light_detection/traffic_light_training.py
```

works now.

# Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works (might be obsolete with CI later on)
- [x] New and existing unit tests pass locally with my changes (might be
obsolete with CI later on)

build/docker-compose.yml

@@ -65,9 +65,10 @@ services:
  - /tmp/.X11-unix:/tmp/.X11-unix
  # if you change the volume here also change the copy command
  # in ``build/docker/build/Dockerfile
- - ../:/workspace
+ - ../code:/workspace/code
  # mount git config for dvc
  - ../.gitconfig:/home/carla/.gitconfig
+ - ../:/workspace/
  networks:
  - carla
  - ros