Convert and concatenate ALFA results for MultiQC report

Currently, results of ALFA are .pdf files. However, the MultiQC report #23 (closed) only support a single .png per section.

Therefore, the ALFA results should be converted with imagemagick container: https://hub.docker.com/r/zavolab/imagemagick and concatenated.

The final plot is in directory results/ALFA/.

• The result for test_integration is ALFA_plots.concat.png
• result for test_alfa is ALFA_plots.concat.png

mentioned in commit 1e6909b0

closed via merge request !52 (merged)

mentioned in commit 9d010052