Write tests for code in src/common/

[markus-hinsche]

We have a very low test coverage: (see https://dev.azure.com/cgmorg/ChildGrowthMonitor/_build/results?buildId=449&view=logs&j=19c563d8-3dcd-57d1-cd5e-9dd946b0a29b&t=c276ab56-9c7b-560d-e018-453666437518&l=68) and we even just test a portion of the files.

Especially for code in src/common this would help.

[lvonasek]

I added a US for depthmap toolkit: https://dev.azure.com/cgmorg/ChildGrowthMonitor/_workitems/edit/337 I assigned it to me but I will definitely need there some help

[markus-hinsche]

We need unit tests for src/common/rgbd_toolkit/

[jasminziegler]

I increased our test coverage in PR #353