requirements.txt has issues/conflicts

I think the whole requirements.txt needs to be reviewed for a fresh install. Multiple dependencies rely on each other and are causing errors.

Firstly

```
ERROR: Could not find a version that satisfies the requirement opencv-python-headless==4.2.0.32 (from -r requirements.txt (line 3)) (from versions: 3.4.10.37, 3.4.11.39, 3.4.11.41, 3.4.11.43, 3.4.11.45, 3.4.13.47, 3.4.14.51, 3.4.14.53, 4.3.0.38, 4.4.0.40, 4.4.0.42, 4.4.0.44, 4.4.0.46, 4.5.1.48, 4.5.2.52, 4.5.2.54)
ERROR: No matching distribution found for opencv-python-headless==4.2.0.32 (from -r requirements.txt (line 3))
```

then by upgrading to `opencv-python-headless==4.3.0.38` we get:

```
ERROR: Cannot install -r requirements.txt (line 3) and numpy==1.17.2 because these package versions have conflicting dependencies.

The conflict is caused by:
The user requested numpy==1.17.2
opencv-python-headless 4.3.0.38 depends on numpy>=1.17.3

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies
```

There were also other issues within running `pip3 install -r requirements.txt`

Cheers