slim docker image for `imagemagick`

During our fun debugging time me and @boersch noticed that rhea breaks when executed on real data - regardless if running on the cluster or locally. The breaking rule is alfa_concat_results and it is because imagemagick raises an error: convert: cache resources exhausted. The memory limits are tool low. I have resolved that issue by reverting to the older image we have @ dockerhub. So the associated change in Snakefile is:

    singularity:
        "docker://zavolab/imagemagick:7.0.8"

instead of:

    singularity:
        "docker://zavolab/imagemagick:6.9.10-slim"

for that particular rule.

If you still want to 'slimify it' please be aware that you might end up with something that passes integration tests but fails on real data...

=====EDIT=====
It is about internal memory limits in the configs of imagemagick - not related to our cluster in any sense.